Semiconductor device and semiconductor device producing system

ABSTRACT

An insulating film having depressions and projections are formed on a substrate. A semiconductor film is formed on the insulating film. Thus, for crystallization by using laser light, a part where stress concentrates is selectively formed in the semiconductor film. More specifically, stripe or rectangular depressions and projections are provided in the semiconductor film. Then, continuous-wave laser light is irradiated along the stripe depressions and projections formed in the semiconductor film or in a direction of a major axis or minor axis of the rectangle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device including asemiconductor film having a crystal structure and particularly to asemiconductor device including a crystalline semiconductor film raisedon an insulating surface and a field-effect transistor such as a thinfilm transistor and/or a bipolar transistor especially. In addition, thepresent invention relates to a semiconductor device producing system forcrystallizing a semiconductor film by using laser light and foractivating a semiconductor film after ion implantation.

2. Description of the Related Art

A technology has been known for crystallizing an amorphous semiconductorfilm over a substrate of, for example, glass through laser processing.The laser processing may be a technology for re-crystallizing a damagedlayer or an amorphous layer on a semiconductor substrate or asemiconductor film, a technology for crystallizing an amorphoussemiconductor film on an insulating surface, or a technology forimproving the crystallinity of a semiconductor film having a crystalstructure (crystalline semiconductor film). A laser oscillating deviceused for the laser processing generally uses gaseous laser such asexcimer laser or solid laser such as YAG laser.

Laser beam is used because an area absorbing energy from irradiatedlaser beam can be. heated selectively in comparison with heat processingusing radiant heating or conductive heating. For example, laserprocessing using excimer laser oscillating device for oscillating ultraviolet light having a wave length equal to or less than 400 nm heats asemiconductor film selectively and locally. Then, crystallization and/oractivation processing can be performed on the semiconductor film byhardly damaging the glass substrate thermally.

JP Laid-Open 62-104117 (page 92) discloses laser processing in which anamorphous semiconductor film is crystallized without melting thesemiconductor film completely by adopting rapid scanning using laser of(beam spot diameter×5000)/second or more. U.S. Pat. No. 4,330,363 (FIG.4) discloses laser processing in which an extended laser beam isirradiated to an island-shaped semiconductor area to form a singlecrystalline area essentially. Alternatively, JP Laid-Open 8-195357(Pages 3 to 4 and FIGS. 1 to 5) discloses a method in which a beam to beirradiated is processed linearly by an optical system such as a laserprocessing apparatus.

Furthermore, for example, JP Laid-Open 2001-144027 (Page 4) discloses acrystallization technology using a solid laser oscillating device with,for example, Nd: YVO₄ laser. According to the technology, a secondharmonic of a laser beam projected from the solid laser oscillatingdevice is used such that a crystalline film having a larger crystalgrain size than the conventional size can be obtained to be applied fora thin. film transistor (called “TFT” hereinafter).

The application to a thin film transistor (called “TFT” hereinafter) inthe crystallization technology using the solid laser oscillating deviceis reported in A. Hara, F. Takeuchi, M. Takei, K. Yoshino, K. Suga andN. Sasaki, “Ultra-high Performance Poly-Si TFT on a Glass by a StableScanning CW Laser Lateral Crystallization”, AMLCD ” 01 Tech. Dig., 2001,pp. 227-230. According to the result described in the document, a secondharmonic wave of a diode-excited solid continuous wave laser (YVO₄) isused to crystallize an amorphous silicon film to be used for producing aTFT.

Conventionally, improvement in TFT characteristics may have requiredimprovement in crystallinity of the active layer (which is asemiconductor film including regions and/or a semiconductor film havingsource or drain regions, here).

Forming a single crystalline semiconductor on an insulating surface hasbeen attempted for a long time. A technology called Graphoepitaxy wasdesigned as a more active attempt. According to Graphoepitaxy, gradechanges are formed on a surface of a quartz substrate. Then, anamorphous film or a polycrystalline semiconductor film is formedthereon. By heating it by using a laser beam or a heater, an epitaxialgrowing layer is formed by having the grade change on the quartzsubstrate as a core. The technology is disclosed in J. Vac. Sci.Technol., “Grapho-epitaxy of silicon on fused silica using surfacemicropattems and laser crystallization”, 16(6), 1979, pp. 1640-1643, forexample.

In addition, M. W. Geis, et al., “CRYSTALLINE SILICON ON INSULATORS BYGRAPHOEPITAXY” Technical Digest of International Electron DevicesMeeting, 1979, pp. 210 discloses a semiconductor film crystallizationtechnology called graphoepitaxy. The technology attempts epi-raising ofa semiconductor film by inducing grade changes on a surface of anartificial amorphous substrate. In the graphoepitaxy disclosed in thedocument, grade changes are provided on a surface of an insulating film,and processing including heating or irradiating laser light is performedon a semiconductor film on the insulating film. Thus, crystal of thesemiconductor film is epitaxially raised.

However, in order to form a semiconductor film having good crystallinitywith fewer defects and/or crystal grain boundaries and with uniformalignment, a semiconductor is conventionally and mainly heated to ahigher temperature to be melted and then is crystallized. This is knownas a band melting method.

According to the publicly-known graphoepitaxy technology, grade changesin a primary layer is used. Thus, crystal grows along the grade changes.As a result, the grade changes remain on the surface of the formedsingle crystalline semiconductor film disadvantageously. Furthermore, asingle crystalline semiconductor film cannot be formed by using thegraphoepitaxy on a large glass substrate having smaller distortionpoints.

In all of the cases, a crystalline semiconductor film having fewerdefects cannot be formed due to the volume shrinkage of thesemiconductor, thermal stresses against the base, grating mismatch andso on caused by crystallization. Furthermore, distortions areaccumulated. Thus, an area causing defects cannot be positionallycontrolled so as to position in the other area than element formingareas. Accordingly, without bonded SOI (silicon on insulator), acrystalline semiconductor film on an insulating surface cannot obtainthe same quality as that of a MOS transistor provided on a singlecrystalline semiconductor.

SUMMARY OF THE INVENTION

The present invention was made in view of these problems. It is anobject of the present invention to provide a semiconductor deviceincluding a fast semiconductor element having a higher current drivingability for forming a uniform crystalline semiconductor film, and,preferably, a single crystalline semiconductor film on a glass substratehaving fewer distortion points.

Recently, technologies each for forming a TFT over a substrate have beenevolved significantly. The technologies have been applied to the activematrix type semiconductor display device. Especially, a TFT using apolycrystalline semiconductor film has higher field effect mobility thanthat of a TFT having a conventional amorphous semiconductor film.Therefore, rapid operations are possible. Thus, pixel control, which hasbeen performed by a drive circuit provided outside of a conventionalsubstrate, can be performed by a drive circuit over a substrate on whichpixels are also provided.

By the way, a glass substrate is preferred for a semiconductor device toa single crystalline silicon because of the costs. A glass substrate haslow heat resistance and may be deformed by heat easily. Therefore, whena polysilicon TFT is formed on a glass substrate, laser-annealing may beused for crystallizing the semiconductor film. Thus, heat-deformation ofthe glass substrate can be avoided very effectively.

In comparison with an annealing method used for radiant-heating orconductive heating, laser annealing can reduce a processing timesignificantly. In addition, a semiconductor or a semiconductor film isheated selectively and locally, which can hardly damage the substratethermally.

The “laser-annealing” herein refers to a technology for recrystallizinga damaged layer on a semiconductor substrate or on a semiconductor filmor a technology for crystallizing a semiconductor film over a substrate.In addition, the “laser-annealing” herein includes a technology to beapplied for planarizing or improving the quality of the surface of asemiconductor substrate or a semiconductor film. A laser oscillatingdevice to be applied may be a gaseous laser oscillating device such asexcimer laser, a solid laser oscillating device such as YAG laser. Theseapparatus can heat a surface layer of a semiconductor for a very shortperiod of time as much as several tens nano to several tens micro byirradiating laser light thereon such that the surface layer can becrystallized.

Lasers may be divided into two including those of a pulse type and of acontinuous wave type. The pulse type of laser outputs higher energy.Therefore, the mass production characteristic can be improved by using alaser beam of several cm in size or more. Especially, the form of thelaser beam may be processed by using an optical system so as to obtain alinear shape of 10 cm long or more. Then, the laser light can beirradiated to a substrate efficiently. As a result, the mass productioncharacteristic can be further improved. Accordingly, using the pulsetype of laser for the semiconductor film crystallization is becoming amain stream.

However recently, when the continuous wave type of laser is used forcrystallizing a semiconductor film, crystal formed within asemiconductor film is found larger in grain size than those obtained byusing the pulse type of laser. The larger the crystal grain size iswithin a semiconductor film, the higher the mobility of a TFT formed byusing the semiconductor film is. Therefore, the serial oscillating typeof laser starts to gather attentions gradually.

A crystalline semiconductor film produced by using laser annealing,including those of the pulse type and the continuous wave type, areformed by gathering multiple crystal grains in general. The positionsand sizes of the crystal grains are random. Therefore, a crystallinesemiconductor film is difficult to form by specifying the positions andsizes of the crystal grains. As a result, an active layer formed bypatterning the crystalline semiconductor into an island shape may haveinterfaces (grain boundaries) between crystal grains.

Unlike the inside of the crystal grain, the grain boundary hasnumberless centers of recombination and/or capture due to an amorphousstructure or defective crystal. When a carrier is trapped by the centerof capture, the potential at the grain boundary increases, which is abarrier against the carrier. Therefore, the current transportationcharacteristic of the carrier is reduced. Accordingly, when a grainboundary exists in a channel-forming region especially, thecharacteristics of the TFT may be affected significantly. The mobilityof the TFT is significantly decreased. ON-current is reduced, and OFFcurrent is increased because current flows at the grain boundary. Thecharacteristics of multiple TFT produced for obtaining the samecharacteristics may vary depending on the presence of the grain boundaryin the active layer.

When laser light is irradiated to a semiconductor film, the obtainedcrystal grains have random positions and sizes. The reasons are asfollows: A certain period of time is required until a solid phase coreis created in a liquid semiconductor film, which has been meltedcompletely by the irradiation of the laser light. With a lapse of time,numberless crystal cores are caused in the completely-melted area. Then,crystal grows from the crystal cores. The crystal cores are caused atrandom positions. Therefore, the crystal cores range nonuniformly. Thecrystal finishes growing when the crystal grains touch each other.Therefore, the crystal grains in random size are caused at randompositions.

Ideally, the channel-forming region affecting the characteristics of theTFT significantly is removed such that a single crystal grain can beformed. Forming an amorphous silicon film having no grain boundaries hasbeen almost impossible by using laser annealing. Even today, a TFTcannot be obtained which has, as an active layer, a crystalline siliconfilm crystallized by using laser annealing and has the samecharacteristics as those of a MOS transistor produced on a singlecrystalline silicon substrate.

The present invention was made in view of these problems. It is anotherobject of the present invention to provide a system of producing asemiconductor device by using a laser crystallizing method, which canprevent grain boundaries from forming in a channel-forming region of aTFT and which can prevent a significant increase in mobility, a decreasein ON-current, and/or an increase in OFF-current of a TFT due to thegrain boundaries.

In order to solve these problems, according to the present invention,multiple insulating films are stacked. Alternatively, on a primaryinsulating film having rectangular or strip grade changes formed bychemically engraving a pattern on an insulating film, an amorphoussemiconductor film or a crystalline semiconductor film is formed. Then,a laser beam is irradiated thereto for crystallization. Then, at leastthe crystalline semiconductor film in depression bottom portions of theprimary insulating film is left. Then, a TFT is formed such that achannel forming region can be provided in the crystalline semiconductorfilm. The channel forming region extends longitudinally in thedepression bottom portion of the rectangular or a strip grade change.

The primary insulating film having the grade changes is formed by usingsilicon nitride, silicon oxide, silicon nitride oxide or silicon oxidenitride. The grade change may be formed by etching the film or may beformed by stacking multiple films. In the present invention, the siliconnitride oxide contains oxygen of not less than 20 atomic % to not morethan 30 atomic % in density, nitrogen of not less than 20 atomic % tonot more than 30 atomic % in density and hydrogen of not less than 10atomic % to not more than 20 atomic % in density. The silicon oxidenitride contains oxygen of not less than 55 atomic % to not more than 65atomic % in density, nitrogen of not less than 1 atomic % to not morethan 20 atomic % in density and hydrogen of not less than 0.1 atomic %to not more than 10 atomic % in density.

The rectangular or strip grade change is formed by forming a firstinsulating film containing silicon oxide or silicon oxide nitride allover a substrate and forming a second insulating film containing siliconnitride or silicon nitride oxide in a rectangular or strip pattern.Alternatively, a second insulating film, which is silicon oxide nitridefilm, is formed all over a first insulating film formed by using arectangular or strip pattern of silicon nitride, silicon oxide, siliconnitride oxide or silicon oxide nitride.

Originally, a silicon nitride film has large stress. Therefore, when acrystalline semiconductor film is formed thereon, distortion isundesirably formed due to the stress effect. A silicon oxide film hassmaller internal stress. Therefore, the crystalline semiconductor filmand an interface can be kept in better contact. As a result, theinterface level density can be reduced. Silicon oxide nitride has acharacteristic combining an impurity blocking characteristic of siliconnitride with characteristics of silicon oxide. Thus, the internal stresscan be controlled to be smaller. Therefore, silicon oxide nitride filmis suitable for the primary insulating film.

The grade changes are formed in accordance with an alignment of TFTsover a substrate surface and does not have to be in a regular andcyclical pattern. According to the present invention, each of the gradechanges in a primary insulating film acts effectively by locallyconcentrating stress from volume shrinkage caused by crystallizationsuch that stress distortion cannot occur on an active layer, especially,a channel-forming region of a semiconductor element.

In a process for crystallizing an amorphous semiconductor film, volumeshrinkage occurs due to realignment of atoms and/or separation ofcontained hydrogen. The percentage depends on conditions for producingthe amorphous semiconductor film but may be regarded as about 0.1% to1%. As a result, tensile stress occurs in the crystalline semiconductorfilm. The size may be about 1×10¹⁰ dyn/cm². This is significant in anamorphous silicon film containing hydrogen, for example. Therefore, whena crystalline semiconductor film is re-crystallized, the same phenomenonmay occur. The stress due to the crystallization concentrates on thegrade change and may be stored as internal stress. Alternatively, thestress can cause a crack.

The part storing the distortion may be applied partially. Channelforming regions are provided in crystalline semiconductor films indepression bottom surfaces on a primary insulating film having multiplerectangular or strip grade changes, respectively. Each of thechannel-forming regions may extend in a longitudinal direction of thestrip grade change and may connect to the crystalline semiconductorfilm. A source region or a drain region may be formed in thecontinuously-formed crystalline semiconductor film. With this form, amulti-channel TFT is formed having multiple channel-forming regions inone TFT.

Alternatively, multiple rectangular semiconductor regions placed inparallel are connected in series. A crystalline semiconductor film isintegrally formed by using a pair of semiconductor regions connected atthe both ends. In the multiple rectangular semiconductor regions,channel forming regions are formed with electrodes crossing through aninsulating film. Crystal extends in the channel length direction.

For crystallization using grade changes formed on the primary insulatingfilm, laser beams to be gathered linearly are irradiated by using acontinuous wave type laser oscillating device. The laser beams desirablyhave an energy density distribution in which the strength distributionis uniform in the longitudinal direction. The distribution in thetransverse direction may be arbitrary and, for example, may haveGaussian distribution. The laser processing is performed by scanning ina direction crossing the longitudinal direction of the continuous wavelaser beams to be gathered linearly. Here, if the laser beams have auniform strength direction in the longitudinal direction. Crystal growthextending in parallel with the scanning direction can be achieved. Inother words, when the energy density distribution is not uniform in thelongitudinal direction, a temperature gradient may occur. Then, crystalis formed having crystal grain boundaries extend by depending thereon.

The light source of the continuous wave laser beam is a rectangular beamsolid laser oscillating device. Typically, a slab laser oscillatingdevice may be applied.

In view of the light absorbing coefficient, the semiconductor film isheated by the irradiation of laser beams substantially selectively. Thesemiconductor melted by the irradiation of laser beams is crystallizedat when it is set. Different heat capacities occur due to the gradechanges in the primary insulating film. A side end portion where thefirst insulating film and the second insulating film overlap cools offthe fastest. Crystal can be raised from the side end portion.

Crystal in the rectangular semiconductor region having channel formingregions extends in a direction parallel to the channel length direction.The crystal orientation is uniform.

In other words, the region for forming the channel forming region of theTFT may be formed on the projection top portion of the primaryinsulating film. Thus, good crystal can be used selectively.Alternatively, the region where distortion concentrates most in thegrade change portion may be removed from the channel forming region.

In this construction, multiple rectangular semiconductor regions areplaced in parallel between a pair of source and drain regions. As aresult, one transistor can be formed. Therefore, the distribution ofcharacteristics between elements can be suppressed. By usinggood-quality crystal only, the field effect mobility can be improved.

The “amorphous semiconductor film” herein refers to not only one havinga complete amorphous structure in the narrow sense but also thesemiconductor film containing fine crystal particles, a so-calledmicrocrystal semiconductor film or a semiconductor film having a crystalstructure locally. Typically, an amorphous silicon film is applied.Additionally, a silicon germanium film or an amorphous silicon carbidemay be applied.

The inventors found that the direction of stress caused in asemiconductor film closely related to a position and orientation ofgrain boundary when the semiconductor film was crystallized by theirradiation of laser light. FIG. 1A shows a section image of TEM in adirection perpendicular to the scanning direction of laser light. Inthis case, continuous oscillating laser light is irradiated to anamorphous semiconductor film of 200 mm in thickness at a scanning speedof 5 cm/sec. In FIG. 1A, widths of crystal grain boundaries 10 a, 10 band 10 c in the direction perpendicular to the scanning direction arerandom.

FIG. 1B schematically shows the section image of TEM shown in FIG. 1A.As shown in FIG. 1B, a semiconductor film 102 has projections betweenthe grain boundary 10 a and the grain boundary 10 b and between thegrain boundary 10 b and the grain boundary 10 c. The inventorsconsidered that, as indicated by arrows, stress was imposed in adirection parallel to the substrate from near the grain boundary to thecenter of the crystal grain.

Thus, the inventors estimated that the position at which a grainboundary was formed could be determined selectively by intentionallyforming in the semiconductor film a part on which stress was extensivelyimposed. Thus, according to the present invention, an insulating filmhaving depressions and projections is formed on a substrate. Then, asemiconductor film is formed on the insulating film. Thus, a part onwhich stress is extensively imposed during the crystallization by laserlight is selectively formed in the semiconductor film. Morespecifically, stripe (or strip) or rectangular depressions andprojections are provided in the semiconductor film. Continuous wavelaser light is irradiated along the stripe depressions and projectionsformed in the semiconductor film or in the major axis or minor axis ofthe rectangle. In this case, the continuous wave laser light is the mostpreferably used. However, pulse laser light may be used. A section ofthe depression in a direction perpendicular to the scanning direction oflaser light may be rectangle, triangle or trapezoid.

During the crystallization by the laser light irradiation, stressconcentrates near the edges of the depressions or near the edges ofprojections in the semiconductor film. As a result, a grain boundary isformed. Smaller stress occurs near the center of the projection or nearthe center of the depression in the semiconductor than near the edges ofthe depression or near the edges of projection. Thus, grain boundariesmay be more hardly formed. Even when a grain boundary is formed, thecrystal grain is large. Therefore, good crystallinity can be obtained.

According to the present invention, after the crystallization by laserlight, the part near the edges of the depression or near the edges ofthe projection in the semiconductor film is removed by patterning. Then,a part having good crystallinity near the center of the depression maybe used actively as an active layer of the TFT. As a result, grainboundaries may be prevented from forming in the channel forming regionof the TFT. Thus, a significant increase in mobility, a decrease inON-current, and/or an increase in OFF-current of the TFT due to grainboundaries may be prevented. The area to be removed by patterning nearthe edges of the depression may be determined by the designer.

Generally, the energy density near the edge of a laser beam of laserlight is lower than the energy density near the center. Therefore, thecrystallinity of the semiconductor film may be lower Therefore, whenscanning laser light, the part to be a channel forming region of the TFTlater, more preferably, the depression of the semiconductor film and theedge of the trace must be prevented from overlapping with each other.

Accordingly, in a producing system of the present invention, data(pattern information) of a form of an insulating film or a semiconductorfilm viewed from above the substrate, which is obtained while designing,is stored in a storage device. A scanning path of laser light isdetermined based on the pattern information and a width in a directionperpendicular to the scanning direction of the laser beam of laserlight. Thus, at least a part to be a channel forming region of the TFTmay not overlap with the edge of the trace of the laser light. Thesubstrate may be positioned with reference to a marker. Then, laserlight is irradiated to a semiconductor film on the substrate byfollowing the determined scanning path.

With this construction, laser light may be scanned to at least arequired part without irradiating laser light to the entire substrate.Therefore, a time for irradiating laser light to unnecessary parts canbe saved. As a result, a time for laser light irradiation can bereduced. The speed for processing the substrate can be improved.Damaging the substrate due to the irradiation of laser light tounnecessary parts can be prevented.

The marker may be formed by etching the substrate with laser lightdirectly. Alternatively, when an insulating film having depressions andprojections is formed, the marker may be formed at a part of theinsulating film at the same time. A form of the actually formedinsulating film or semiconductor film may be read by using an imagingelement such as a CCD and may be stored in a first storage unit as data.Pattern information of the insulating film or semiconductor filmobtained while designing may be stored in a second storage unit. Then,by comparing the data stored in the first storage unit and the patterninformation stored in the second storage unit, the substrate may bepositioned.

When a form of a semiconductor film is read, the semiconductor filmitself has a certain amount of thickness. Therefore, the form of thesemiconductor film does not always match with a mask of the insulatingfilm. Thus, the comparison with pattern information should be performedin consideration of the thickness of the semiconductor film. A CCD maynot be always used for identifying the form. For example, laser lightemitted from a laser diode may be irradiated to the insulating film orsemiconductor film. Then reflected light may be monitored to identifythe form.

By forming a marker at a part of the insulating film and/or by using aform of the insulating film as a marker, one mask for the marker can beeliminated. Furthermore, a marker can be formed at a more preciseposition in comparison with a case where a marker is formed on thesubstrate by laser light. Therefore, the precision of the positioningcan be improved.

The energy densities of a laser beam of laser light is not completelyuniform in general, and the height depends on the position within thelaser beam. In the present invention, laser light with a uniform energydensity must be irradiated to at least a part to be a channel formingregion and, more preferably, to an entire flat surface of thedepression. Therefore, in the present invention, a laser beam to be usedis required to have an energy density distribution in which, by laserlight scanning, an area having a uniform energy density overlaps with atleast a part to be a channel forming region, and, more preferably, withan entire flat surface of the depression. In order to satisfy the energydensity requirement, the laser beam is desirably rectangular or linear.

Additionally, a part with a lower energy density in a laser beam can beblocked by a slit. By using the slit, laser light with a more uniformenergy density can be irradiated to the entire flat surface of thedepression. Therefore, uniform crystallization can be achieved. The slitcan be used to change a width of a laser beam partially based on patterninformation of the insulating film or semiconductor film. Thus,constraints on the layout of channel forming regions and furthermore anactive layer of the TFT can be reduced. The “width of a laser beam”refers to a length of a laser beam in a direction perpendicular to ascanning direction.

One laser beam obtained by combining laser light oscillated frommultiple laser oscillating devices may be used for lasercrystallization. With the construction, a part having a lower energydensity in each laser light can be compensated.

After a semiconductor film is formed, the semiconductor film may becrystallized by irradiating light thereto so as to prevent thesemiconductor film from exposing to the air (that is, in an atmosphereof specified gas such as rare gas, nitrogen and oxygen or in areduced-pressure atmosphere). With the construction, a contaminationmaterial at a molecule level in a clean room such as boron containedwithin a filter for improving cleanness of the air, for example, isprevented from intruding into the semiconductor film during thecrystallization by laser light.

In a semiconductor film crystallization technology called graphoepitaxydisclosed in the document, J. Vac. Sci. Technol., “Grapho-epitaxy ofsilicon on fused silica using surface micropattems and lasercrystallization”, 16 (6), 1979, pp 1640-1643, or in the document, M. W.Geis, et al., “CRYSTALLINE SILICON ON INSULATORS BY GRAPHOEPITAXY”Technical Digest of International Electron Devices Meeting, 1979, pp.210, epitaxial growth requires a temperature of at least about 700° C.When epitaxial growth is attempted on a glass substrate, grainboundaries are formed in a semiconductor film near edges of depressionsin an insulating film. According to the present invention, a mask for anisland is laid out. Then, in order to improve crystallinity at a part tobe the island, a form of the depression of the insulating film andpositions of the edges are designed in accordance with the layout of theisland. More specifically, the form, size and so on of the depressionare determined such that the edges of the depression and the islandcannot overlap with each other. Then, an insulating film designed inaccordance with the island layout is used, and a semiconductor film isformed in which grain boundaries are intentionally formed near theedges. Then, parts of the semiconductor film, which has many grainboundaries near the edges, are removed by patterning. Then, a parthaving better crystallinity is used as an island. Accordingly, thetechnology disclosed in the present invention agrees with theconventional graphoepitaxy in that a semiconductor is formed on aninsulating film having grade changes and the semiconductor film iscrystallized by using the grade changes. However, the conventionalgraphoepitaxy does not include a concept that positions of grainboundaries are controlled by using grade change to reduce the number ofgrain boundaries within an island. Therefore, the present invention iscompletely different from the conventional graphoepitaxy.

As described above, according to the present invention, by following apattern in a primary insulating film having grade changes, a crystallinesemiconductor film is left on the top of the projection. Then, the leftcrystalline semiconductor film is used as an active layer of a TFT.Thus, good crystal can be used selectively. In other words, distortionareas concentrating on the grade changes can be removed from a channelforming region.

In crystallization by irradiating a continuous wave laser beam to anamorphous semiconductor film, distortion and/or stress resulting fromthe crystallization can be concentrated on grade changes provided in theprimary insulating film. Therefore, the distortion and/or stress areprevented from imposing on the crystalline semiconductor to be an activelayer. Then, a TFT can be formed in which channel forming regions areprovided in the crystalline semiconductor film free from the distortionand/or stress. As a result, current driving ability can be improvedfast, and the reliability of elements can be improved.

Furthermore, variations in characteristic of the TFT, more specifically,S-values, mobility and threshold values of the TFT, can be suppressed.

According to the present invention, after crystallization with laserlight, parts near the edges of depressions or near the edges ofprojections in the semiconductor film are removed by patterning. Then,parts having good crystallinity near the centers of the depressions maybe used actively as an active layer of the TFT. Thus, a significantdecrease in mobility, a decrease in ON-current and/or an increase in OFFcurrent of the TFT due to the grain boundaries can be prevented. Theranges to be patterned and to be removed near the edges of thedepressions may be determined by the designer appropriately.

Laser light is not scanned and irradiated on the semiconductor filmentirely. However, laser light may be scanned for crystallizing at leasta minimum required part. With the construction, a time for irradiatinglaser light to a part to be removed by patterning after thesemiconductor film is crystallized can be saved. As a result, theprocessing time taken for one substrate can be reduced significantly.

Multiple laser light beams are overlapped to compensate each other forthe parts with lower energy densities. Thus, crystallinity of thesemiconductor film can be improved efficiently by overlapping multiplelaser light beams rather than using the laser light beams separately.

Rather than forming depressions and projections in the insulating film,depressions and projections may be provided in the substrate itself byetching. Thus, a semiconductor film to be formed on the substrate canhave depressions and projections. As a result, parts causing stressconcentration may be formed intentionally.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a TEM sectional image and a schematic sectionaldiagram of a crystallized semiconductor film;

FIGS. 2A to 2D show states where laser light is irradiated to asemiconductor film;

FIGS. 3A to 3C show an island formed by patterning a crystallizedsemiconductor film;

FIGS. 4A and 4B show a construction of a TFT formed by using the islandshown in FIG. 3;

FIG. 5 is flowchart of a producing system according to the presentinvention;

FIG. 6 shows a laser irradiating apparatus;

FIG. 7 shows a laser irradiating apparatus;

FIGS. 8A to 8D show how an insulating film having projections anddepressions is produced;

FIGS. 9A to 9C show how an insulating film having projections anddepressions is produced;

FIGS. 10A to 10C show an island formed by patterning a crystallizedsemiconductor film;

FIGS. 11A and 11B show insulating films having depressions andprojections;

FIGS. 12A to 12D are a top view and sectional views of a TFT formed byusing the insulating film shown in FIG. 11B;

FIGS. 13A to 13D show a method of producing a semiconductor deviceaccording to the present invention;

FIGS. 14A to 14C show a method of producing a semiconductor deviceaccording to the present invention;

FIGS. 15A to 15C show a method of producing a semiconductor deviceaccording to the present invention;

FIG. 16 shows a method of producing a semiconductor device according tothe present invention;

FIG. 17A to 17E show a method of crystallizing a semiconductor film;

FIGS. 18A to 18D show distributions of energy densities of laser beams;

FIGS. 19A and 19B show distributions of energy densities of laser beams;

FIG. 20 shows a distribution of energy densities of a laser beam;

FIG. 21 shows an optical system;

FIGS. 22A to 22C show optical systems;

FIG. 23 shows a distribution of energy densities in a direction of acenter axis of superimposed laser beams;

FIG. 24 shows a relationship between a distance and energy differencesbetween centers of laser beams;

FIG. 25 shows distributions of output energy in a direction of centeraxes of laser beams;

FIG. 26 is a perspective diagram for explaining a construction of asemiconductor device and a method of producing the semiconductor deviceaccording to the present invention;

FIG. 27 is a perspective diagram for explaining a construction of asemiconductor device and a method of producing the semiconductor deviceaccording to the present invention;

FIG. 28 is a perspective diagram for explaining a construction of asemiconductor device and a method of producing the semiconductor deviceaccording to the present invention;

FIG. 29 is a perspective diagram for explaining a construction of asemiconductor device and a method of producing the semiconductor deviceaccording to the present invention;

FIGS. 30A to 30C are vertical section diagrams for explaining details ofcrystallization according to the present invention;

FIGS. 31A and 31B are arrangement diagrams showing a form of laserirradiating apparatus to be applied to the present invention;

FIGS. 32A to 32F are vertical section diagrams for explaining a methodof producing a semiconductor device according to the present invention;

FIG. 33 is a vertical section diagram for explaining the method ofproducing the semiconductor device according to the present invention;

FIG. 34 is a top view for explaining a detail of crystallizationaccording to the present invention;

FIG. 35 is a top view for explaining a method of producing asemiconductor device according to the present invention;

FIG. 36 is a top view for explaining a method of producing asemiconductor device according to the present invention;

FIG. 37 is an equivalent circuit diagram corresponding to the top viewof the TFT shown in FIG. 36;

FIGS. 38A to 38C are vertical section diagrams for explaining details ofcrystallization according to the present invention;

FIGS. 39A to 39C show vertical section diagrams for explaining methodsof producing a primary insulating film and an amorphous semiconductorfilm according to the present invention;

FIGS. 40A to 40C show vertical section diagrams for explaining methodsof producing a primary insulating film and an amorphous semiconductorfilm according to the present invention;

FIG. 41 is an external view of a display panel;

FIG. 42 is a top view for explaining a construction of a pixel portionof the display panel;

FIGS. 43A to 43G show examples of the semiconductor device;

FIGS. 44A to 44D show examples of a projector;

FIGS. 45A to 45C show S-value frequency distributions;

FIGS. 46A to 46C show threshold value frequency distributions;

FIGS. 47A to 47C show mobility frequency distributions;

FIGS. 48A to 48C show threshold values frequency distributions;

FIGS. 49A to 49C show mobility frequency distributions; and

FIGS. 50A to 50G show steps of producing a semiconductor deviceaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to drawings. A perspective diagram shown in FIG. 26 shows anembodiment having a first insulating film 9102, which is a primaryinsulating film on a substrate 9101, and second insulating films 9103 to9106, which are pattered in a strip form. Here, three depression bottomportions formed by the second insulating films are shown. However, thenumber of the depression bottom portions is not limited thereto. Thesubstrate may be one of a commercially available non-alkali glasssubstrate, quarts substrate, sapphire substrate, a substrate in which asurface of a single crystalline or polycrystalline semiconductorsubstrate is covered by an insulating film, and a substrate in which asurface of a metal substrate is covered by an insulating film.

Preferably, a width W2 of the strip second insulating film is 1 to 10μm. Preferably, a space W1 between the adjacent second insulating filmsis 0.5 to 10 μm, and the thickness is 0.05 to 0.5 μm. The grade changesdo not have to be arranged in a regular cyclical pattern. The gradechanges may be arranged arbitrarily in accordance with a semiconductorelement such as a TFT. A length L of the second insulating film is notlimited and only needs to be a length in which a channel forming regionof a TFT can be formed, for example.

A material of the first insulating film may be a silicon oxide orsilicon oxide nitride. Silicon oxide can be formed by mixing TetraethylOrtho silicate (TEOS) and O₂ and by using Plasma CVD Method. The siliconnitride oxide contains oxygen of not less than 55 atomic % to not morethan 65 atomic % in density, nitrogen of not less than 1 atomic % to notmore than 20 atomic % in density and hydrogen of not less than 0.1atomic % to not more than 10 atomic % in density. The etching rate at20° C. of a mixed solution having density of not less than 6×10²²/cm tonot more than 9×10²²/cm³ and containing ammonium bifluoride (NH₄HF₂) of7.13% and ammonium fluoride (NSF) of 15.4% is 110 to 130 nm/min (90 to100 nm/min after thermal processing at 500° C. for one hour and at 550°C. for four hours). The etching rate defined herein is a value obtainedat 20° C. when liquid solution containing NH₄HF₂ of 7.13% and NH₄F of15.4% is used as the etching solution. The silicon oxide nitride filmmay be formed by using SiH₄ or N₂O and Plasma CVD Method.

A material of the second insulating film may be silicon nitride orsilicon nitride oxide. The silicon nitride oxide contains oxygen of notless than 20 atomic % to not more than 30 atomic % in density, nitrogenof not less than 20 atomic % to not more than 30 atomic % in density andhydrogen of not less than 10 atomic % to not more than 20 atomic % indensity. Alternatively, the composition rate of nitrogen to oxygen isnot less than 0.6 to not more than 1.5. The etching rate at 20° C. of amixed solution having density of not less than 8×10²²/cm³ to not morethan 2×10²³/cm³ and containing ammonium bifluoride (NH₄HF₂) of 7.13% andammonium fluoride (NH₄F) of 15.4% is 60 to 70 nm/min (40 to 50 nm/minafter thermal processing at 500° C. for one hour and at 550° C. for fourhour). The silicon oxide nitride film may be formed by using SiH₄, NH₃or N₂O and Plasma CVD Method.

An angle of a side wall of the grade change formed in the secondinsulating film may be set in a range of 5 to 90 degree. The sectionalform may be not only the rectangular depression-and-projection form butalso a sawtooth depression-and-projection form.

As shown in FIG. 27, the amorphous semiconductor film 9106 of 50 to 200nm in thickness covers the projection top portions, depression bottomportions and grade-change side surfaces of the first insulating film9102 and the second insulating films 9103 to 9015 of the primaryinsulating film. The amorphous semiconductor film is formed by silicon,a compound or alloy of silicon and germanium or a compound or alloy ofsilicon and carbon. Among them, silicon is the most suitable material.

Then, a continuous wave laser beam 9107 is irradiated to the amorphoussemiconductor film 9106 for the crystallization. The laser beam to beapplied is formed by gathering the laser beams linearly by using anoptical system. The strength distribution may have a uniform arealongitudinally and a distribution transversely. A laser oscillatingdevice to be used as an optical source may be a rectangular beam solidlaser oscillating device, and, more preferably, may be a slab laseroscillating device. Alternatively, the laser oscillating device may be asolid laser oscillating device using a rod to which Nd, Tm or Ho isdoped. Especially, the laser oscillating device may be a combination ofa slab-structured amplifier and a solid laser oscillating device usingcrystal obtained by doping Nd, Tm or Ho into crystal such as YAG, YVO₄,YLF and YAlO₃. As shown in an arrow in FIG. 27, scanning is performed ina direction crossing the linear longitudinal direction. In this case,the most preferable scanning is performed in a direction parallel to thelongitudinal direction of the strip pattern on the primary insulatingfilm. The “linear” herein refers to a state where a traverse length to alongitudinal length is 1 to 10 or more.

The slab material may be crystal such as ND: YAG, Nd: GGG (gadoliniumgallium garnet) and Nd: GsGG (gadolinium scandium gallium garnet). Theslab laser travels in a zigzag optical path by repeating totalreflection in the plate-like laser medium.

A wavelength of the continuous wave laser beam is desirably 400 to 700nm in consideration of a light absorbing coefficient of the amorphoussemiconductor film. The light in the wavelength band can be obtained byextracting a second harmonic and a third harmonic of a fundamental waveby using a wavelength converting element. The wavelength convertingelement may be ADP (ammonium dyhydrogen phosphate), Ba₂NaNb₅O₁₅ (bariumsodium niobate), CdSe (cadmium selenide), KDP (kalium dyhydrogenphosphate), LiNbO₃ (lithium niobate), Se, Te, LBO, BBO or KB₅.Especially, LBO is preferably used. In a typical example, a secondharmonic wave (532 nm) of Nd: YVO₄ laser oscillating device (fundamentalwave of 1064 nm) is used. The laser oscillating mode is a single mode,which is TEMOO mode.

Areas of the most suitable silicon have absorbing coefficients 10³ to10⁴ cm⁻¹, as a substantially visible light range. When a substrate ofglass, for example, having higher visible light transmissivity and anamorphous semiconductor film of silicon of 30 to 200 nm in thickness arecrystallized, light having a visible light range having a wavelength of400 to 700 nm is irradiated thereto. Then, the semiconductor area isselectively heated. Thus, the crystallization can be implemented withoutdamaging on the primary insulating film. More specifically, light havinga wavelength of 532 nm can enter to an amorphous semiconductor filmabout 100 nm to 1000 nm. Thus, the light can reach enough to the insideof the amorphous semiconductor film 9106 of 30 nm to 200 nm inthickness. In other words, the semiconductor film can be heated from theinside. Then, almost the whole of the semiconductor film in thelaser-beam-irradiated area can be heated uniformly.

FIGS. 30A to 30C are vertical section diagrams for explaining thecrystallization. As shown in FIG. 30A, the first insulating film 9102,the second insulating films 9103 to 9106 and the amorphous semiconductorfilm 9107 are formed on the substrate 9101. Then, as shown in FIG. 30B,the laser beam 9107 is irradiated thereto for the crystallization. Theboundary portion in contact with the first insulating film 9102 and theside walls of the second insulating films 9103 to 9106 may be cooled andbe hardened the earliest. The crystallization starts from there, andcrystal grows toward the projection top portion. The first insulatingfilm and the second insulating films are stacked on the projection topportion. Therefore, the thermal capacity is larger than and the coolingspeed is lower than those of the other areas. As a result, large crystalgrains can grow. The grade change is stretched in the crystal growingdirection. Due to the shape-related cause, distortion is causedextensively, and the internal stress is accumulated.

This condition is shown in FIG. 30C schematically. Distortion isaccumulated in the grade change 9503 in the crystalline semiconductorfilm 9103. Sometimes, a crack may occur. On the other hand, crystalformed in the depression bottom portion 9502 produces a crystallinesemiconductor film in which distortion is alleviated. The crystallinesemiconductor film formed in this depression bottom portion can beregarded as single crystal or substantial single crystal area.

After the crystallization ends, an active layer 9109 formed by acrystalline semiconductor film is formed by etching as shown in FIG. 28.Channel forming regions 9120 to 9122 (regions surrounded by schematicdotted line) are provided on a depression bottom portion of the primaryinsulating film, that is, on the second insulating films in the activelayer 9109. A grade change area in which crystal grain boundaries and/ordistortion extended from the projection top portion are accumulated isremoved such that crystal cannot occur in the channel forming regions.

In the active layer 9109 shown in FIG. 28, multiple rectangularsemiconductor areas arranged in parallel are integrally formed with apair of semiconductor areas connecting the rectangular semiconductorareas. In each of the multiple rectangular semiconductor areas in theactive layer, electrodes crossing through an insulating film may beprovided. Thus, a channel forming region can be formed there.Alternatively, in this active layer, multiple rectangular semiconductorareas arranged in parallel are connected in series. Then, a pair ofsemiconductor areas connecting at the both ends may be integrallyformed. Then, the multiple rectangular semiconductor areas extend in adirection parallel to the channel length direction. Alternatively, thecrystal directs to the same direction in the channel forming region.

As another embodiment, as shown in FIG. 29, crystalline semiconductorfilm 9110 to 9112 may be formed by corresponding to the secondinsulating films 9103 to 9106. By providing a gate electrode, channelforming regions 9123 to 9125 may be provided in a TFT.

FIGS. 31A and 31B show an example of a construction of a laserprocessing apparatus, which can be applied for crystallization. FIGS.31A and 31B are a front view and an elevation view, respectively, of theconstruction of the laser processing apparatus. The laser processingapparatus includes a laser oscillating device 9301, a shutter 9302, highconversion mirrors 9303 to 9306, a slit 9307, cylindrical lenses 9308and 9309, a mount base 9311, driving units 9312 and 9313 for shiftingthe mount base 9311 in an X direction and in a Y direction, a controlunit 9314 for controlling the driving unit, and an informationprocessing unit 9315 for sending signals to the laser oscillating device9301 and/or the control unit 9314 based on a pre-stored program.

A laser beam gathered by the cylindrical lenses 9308 and 9309 linearlyin a sectional form on the irradiated surface is entered diagonally withrespect to the surface of a substrate 320 of the mount base 9311. Thefocus point is displaced due to the aberration such as astigmaticaberration. Thus, a linear light gathering surface can be formed on theirradiated surface or near the irradiated surface. When the cylindricallenses 9308 and 9309 are made of synthetic quartz, higher transmissivitycan be obtained. The surface of each of the lenses is coated in order toachieve 99% of transmissivity for the wavelength of laser beams.Naturally, the sectional form of the irradiated surface is not limitedto the linear form and may be a rectangle, oval, oblong or the otherarbitrary form. In all of the cases, the ratio of the minor axis to themajor axis falls in a range of 1 to 10 to 1 to 100. A wavelengthconverting element 9310 is provided for obtaining a harmonic wave of afundamental wave.

As described above, a rectangular beam solid laser oscillating device isapplied as the laser oscillating device. More preferably, a slab laseroscillating device is obtained. Alternatively, the laser oscillatingdevice may be a combination of a solid laser oscillating device usingcrystal in which Nd, Tm or Ho are doped to crystal such as YAG, YVO₄,YLF and YAO₃ and a slab-structured amplifier. The slab material may becrystal such as Nd: YAG, Nd: GGG (gadolinium gallium garnet) and Nd:GsGG (gadolinium scandium gallium garnet). Additionally, a gaseous laseroscillating device or a solid laser oscillating device, which canoscillate continuously, may be applied. As the continuous wave solidlaser oscillating device, a laser oscillating device using crystal inwhich Cr, Nd, Er, Ho, Ce, Co, Ti or Tm is doped to crystal such as YAG,YVO₄, YLF and YAO₃. A fundamental wave of an oscillating wavelengthdepends on a material to be doped. However, oscillation is performed byhaving a wavelength of 1 μm to 2 μm. In order to obtain higher outputs,a diode-excited solid laser oscillating device is applied, which can beconnected in a cascade manner.

The mount base 9311 is moved by the driving units 9312 and 9313 indirections of two axes such that laser processing can be performed onthe substrate 9320. The mount base 9311 can be moved by a distancelonger than a length of one side of the substrate 9320 in one directioncontinuously with constant velocity of 1 to 200 cm/sec. and preferably 5to 50 cm/sec. The mount base 9311 can be moved by a distance equal to alongitudinal length of a linear beam in the other directiondiscontinuously and in a stepwise manner The oscillation by the laseroscillating device 9101 and the movement of the mount base 9311 areoperated in synchronous with the information processing unit 9315 havinga microprocessor L The mount base 9311 moves straight in the X directionshown in FIG. 31A such that a laser beam irradiated from a fixed opticalsystem can process an entire surface of the substrate. A positiondetecting means 9316 detects that the substrate 9320 is located at aposition irradiated by the laser beam. Then, the position detecting unit9316 transmits the signal to the information processing unit 9315. Thus,the information processing unit 9315 causes the timing to besynchronized with the oscillating operation by the laser oscillatingdevice 9301. In other words, when the substrate 9320 is not at the laserbeam irradiated position, the laser oscillation is stopped. As a result,the life can be extended.

A laser beam irradiated to the substrate 9320 by the laser irradiatingapparatus having the construction is relatively moved in the X-directionor Y-direction shown in FIGS. 31A and 31B. Thus, the laser beam canprocess a desired area or the entire surface of the semiconductor film.

In this way, for the crystallization by irradiating a continuous wavelaser beam to an amorphous semiconductor film, grade changes areprovided in a primary insulating film. Thus, distortion and/or stresscaused by the crystallization can be concentrated on the grade change.Therefore, the distortion and/or the stress are not imposed on acrystalline semiconductor to be an active layer. A TFT may be formedsuch that a channel forming region can be provided in the crystallinesemiconductor film free from the distortion and/or the stress. Thus, thecurrent driving ability can be improved fast. Then, the reliability ofthe element can be also improved.

Next, a method of irradiating laser light used in the present inventionwill be described with reference to FIGS. 2A to 2D.

First of all, as shown in FIG. 2A, an insulating film 101 is formed on asubstrate 100. The insulating film 101 includes stripe projections 101a. A method of forming the projections and depressions will be describedin detail later. The insulating film 101 may be a silicon oxide film, asilicon oxide nitride film or a silicon nitride film. In this case, theother insulating film may be used which can prevent impurities such asalkali metal from intruding into a semiconductor film to be formedlater, and which has an insulating characteristic resisting atemperature caused by later processing. Additionally, projection anddepressions need to be able to form on the film. Alternatively, astructure stacking two or more films can be adopted.

Here, a marker may be formed by using a part of the insulating film 101simultaneously with forming the insulating film 101.

The substrate 100 only needs to be made of a material resisting aprocessing temperature in later steps. For example, the substrate 100may be a quartz substrate, a silicon substrate, a glass substrate ofbarium borosilicate glass or aluminosilicate glass, or a substrate inwhich an insulating film is formed on a surface of a metal substrate ora stainless substrate. Alternatively, a plastic substrate may be usedwhich is heat-proof resisting the processing temperatures.

Next, a semiconductor film 102 is formed to cover the insulating film101. The semiconductor film 102 can be formed by using a publicly-knownmethod (such as Sputtering method, LPCVD method, and Plasma CVD method).The semiconductor film may be an amorphous semiconductor film, amicrocrystal semiconductor film or a crystalline semiconductor film. Notonly silicon but also silicon germanium may be used.

Here, projections and depressions appear on the semiconductor film 102along the projection and depressions of the insulating film 101. Theprojections 101 a of the insulating film 101 must be formed inconsideration of a thickness of the semiconductor film 102 such thatdepression and projections can appear on the surface of thesemiconductor film 102, which will be formed later.

Next, as shown in FIG. 2A, laser light is irradiated to thesemiconductor film 102. Then, a semiconductor film (after LC) 103 isformed having higher crystallinity. The energy density of the laserlight is lower near an edge of a laser beam 104. Therefore, crystalgrains are smaller near the edge. As a result, a projected part (ridge)appears along the crystal grain boundary. Thus, the edge of a track ofthe laser beam 104 of the laser light is prevented from overlapping witha part to be a channel forming region or a flat surface of a depressionbetween the projections 101 a of the semiconductor film 102.

The scanning direction of the laser light is defined to be parallel witha direction of the projections 101 a, as indicated by an arrow.

In the present invention, publicly known laser can be used. Desirably,the continuous wave laser light is used. However, the effects of thepresent invention can be obtained even if the pulse laser light is used.The laser may be gaseous laser or solid laser. The gaseous laser may beexcimer laser, Ar laser, Kr laser or the like. The solid laser may beYAG laser, YVO₄ laser, YLF laser, YAO₃ laser, glass laser, ruby laser,alexandrite laser, Ti:sapphire laser, Y₂O₃ laser or the like. The solidlaser may be laser using crystal such as YAG, YVO₄, YLF and YAO₃ towhich Cr, Nd, Er, Ho, Ce, Co, Ti, Yb or Tm is doped. A fundamental waveof the laser depends on a material to be doped. Laser light having afundamental wave of around 1 μm can be obtained. A harmonic wave for thefundamental wave can be obtained by using a non-linear optical element.

Infrared laser light emitted from the solid laser is converted to greenlaser light by the non-linear optical element. After that, ultravioletlaser light is obtained by another non-linear optical element. Theultraviolet laser light can be used.

FIG. 2B is a sectional diagram of FIG. 2A taken at a line A-A′, which isbefore crystallization. FIG. 2C is a sectional diagram of FIG. 2A takenat a line B-B′, which is after crystallization. In the semiconductorfilm (after LC) 103 crystallized by laser light irradiation, stressconcentrates near the edges of projections or near the edges ofdepressions. Thus, a grain boundary 105 can occur easily. FIG. 2D showsa magnified diagram of the depression of the semiconductor film 103after crystallization. Arrows indicate directions of internal stress.Stress concentrates at a part 106 near the edge of the projection of thesemiconductor film 103 and a part 107 near the edges of the depressionof the semiconductor film 103. Then, grain boundaries 105 may occur.However, smaller stress occurs in a top flat part of the depression 101a than the stress near the edge of the depression. Therefore, grainboundaries are hard to occur. Even grain boundaries occur, a largercrystal grain can be obtained.

Next, as shown in FIG. 3A, in order to remove the part near the edges ofthe projections or near the edges of the depressions and theprojections, the semiconductor film 103 after crystallization ispatterned. Then, by using a top flat part of the depression between theprojections 101 a having good crystallinity, island-shaped semiconductorfilm (called “island, hereinafter) 108 is formed.

In this example, the semiconductor film 103 is patterned so as to leavethe part near the edges of the projections or near the edges of thedepressions and the projections partly. Thus, as shown in FIG. 3A, eachof the islands 108 is formed to be use as a slit-shaped active layerfrom which a channel forming region is only separated. FIG. 3B shows asection diagram the island 108 taken at a line A-A′. FIG. 3C shows asection diagram of the island 108 taken at a line B-B′. A part to be asource region or a drain region does not have larger effect of thesemiconductor film crystallinity on TFT characteristics than that of thechannel forming region. Therefore, the parts near the edge of theprojection and near the edge of the depression having poor crystallinitymay be left, which is not much problematic.

Next, as shown in FIG. 4A, a gate insulating film 110 is formed so as tocover at least a part to be a channel forming region of the island 108.In FIG. 4A, a part to be a source region or a drain region is exposed.However, the entire island 108 may be covered by the gate insulatingfilm 110.

Next, a conductive film is formed and is patterned in order to form agate electrode 111. FIG. 4B shows a section diagram taken as a line A-A′in FIG. 4A. The gate electrode 111 overlaps with all of the channelforming regions.

Through these production steps, a TFT having multiple channel formingregions, which separate from each other, is completed. With thisconstruction, when a channel width of each of the channel formingregions is long, ON-current can be obtained. At the same time, heatcaused by driving the TFT can be released efficiently.

When a ratio of a channel width of each of the channel forming regionsis W_(ST) and a width between two of the channel forming regions isW_(SO), the ratio between the W_(ST) and the W_(SO) can be set by adesigner as appropriately. More preferably, 3W_(ST) is substantiallyequal to W_(SO).

Next, a producing system according to the present invention will bedescribed. FIG. 5 shows a flowchart of the producing system according tothe present invention. First of all, a mask for the islands is designed.Next, a form of an insulating film is designed to have stripe orrectangular projections and depressions. Here, one or multiple islandsare laid out on a flat surface of the depression of the insulating film.Then, when the islands are used as an active layer of a TFT, thedirection that carriers move is desirably the same as the direction ofthe stripe of the insulating film or the direction of the longer orshorter sides of the rectangle. However, these directions may bedifferentiated intentionally in accordance with the application.

Here, the form of the insulating film may be designed such that a markercan be formed in a part of the insulating film.

Information (pattern information) regarding a form of the designedinsulating film is input to a computer of the laser irradiatingapparatus and is stored in the memory unit. The computer determines alaser light scanning path based on the input insulating film patterninformation and a width in a direction perpendicular to the scanningdirection of a laser beam. In this case, the scanning path needs to bedetermined such that an edge of a track of laser light and a flatsurface of the depression of the insulating film cannot overlap witheach other. In addition to the insulating film pattern information,island pattern information is stored in the memory unit of the computer.Thus, the scanning path may be determined such that an edge of a trackof laser light and the island or the channel forming region of theisland cannot overlap with each other.

When a slit is provided to control a width of a laser beam, the computercan identify a width of the depression of the insulating film in thedirection perpendicular to the scanning direction based on the inputinsulating film pattern information. In consideration of the width ofthe depression of the insulating film, a width of the slit in thedirection perpendicular to the scanning direction is set such that theedge of the track of the laser light and the flat surface of thedepression of the insulating film cannot overlap with each other.

On the other hand, an insulating film is formed on a substrate inaccordance with the designed pattern. Next, a semiconductor film isformed on the insulating film. After forming the semiconductor film, thesubstrate is placed on a stage of the laser irradiating apparatus so asto position the substrate. In FIG. 5, a marker is detected by using aCCD camera to position the substrate. The CCD camera refers to a camerausing charge-coupled device (CCD) as an imaging element.

Alternatively, pattern information of the insulating film or thesemiconductor film on the substrate placed on the stage is detected byusing the CCD camera, for example. Then, the pattern information of theinsulating film or the semiconductor film designed by a CAD in thecomputer is compared with the pattern information of the insulating filmor the semiconductor film formed on the substrate actually, which isobtained by using the CCD camera. Then, the substrate may be positioned.

Then, laser light is irradiated by following a determined scanning pathso as to crystallize the semiconductor film.

Next, after irradiating the laser light, the semiconductor film havingcrystallinity improved by the laser light irradiation is patterned.Thus, an island is formed. After that, a TFT is produced from theisland. The concrete process for producing the TFT depends on the formof the TFT. However, typically, a gate insulating film is deposited, andan impurity region is formed in the island. Then, an interlayerinsulating film is formed so as to cover the gate insulating film and agate electrode. Then, a contact hole is formed in the interlayerinsulating film. A part of the impurity region is exposed. Then, a wireis formed on the interlayer insulating film so as to be in contact withthe impurity region through the contact hole.

Next, a construction of the laser irradiating apparatus used in thepresent invention will be described with reference to FIG. 6. The laserirradiating apparatus includes a laser oscillating device 151. Fourlaser oscillating devices are shown in FIG. 6. However, the number ofthe laser oscillating devices of the laser irradiating apparatus are notlimited thereto.

The laser oscillating device 151 may keep a constant temperature byusing a chiller 152. The chiller 152 is not always necessary. However,keeping the temperature of the laser oscillating device 151 constant canprevent variations in energy of output laser light depending on thetemperature.

The laser irradiating apparatus further includes an optical system 154.The optical system 154 changes an optical path output from the laseroscillating device 151, or processes a form of the laser beam andgathers laser light. In addition, the optical system 154 of the laserirradiating apparatus in FIG. 6 can combine laser beams of laser lightoutput from the multiple laser oscillating devices 151 by overlappingthem partially.

An AO modulator 153, which can change a direction that laser lighttravels in an extremely short period of time may be provided in anoptical path between a substrate 156 to be processed and the laseroscillating device 151. Instead of the AO modulator, an attenuator(light-amount adjusting filter) may be provided to adjust an energydensity of laser light.

An energy density measuring unit 165 may be provided in an optical pathbetween the substrate 156 to be processed and the laser oscillatingdevice 151 for measuring an energy density of laser light output fromthe laser oscillating device 151. Then, changes in the measured energydensity with a lapse of time may be monitored in the computer 160. Inthis case, in order to compensate attenuation in energy density of laserlight, the output from the laser oscillating device 151 may be raised.

The resultant laser beam is irradiated, through a slit 155, to thesubstrate 156. The slit 155 can block laser light and is desirablyformed by a material, which is not deformed or damaged by laser light. Awidth of the slit 155 is variable. A width of a laser beam may bechanged in accordance with the width of the slit.

On the substrate 156, a form of the laser beam of laser light oscillatedfrom the laser oscillating device 151 not through the slit 155 dependson the type of laser. In addition, the form may be defined by using anoptical system.

The substrate 156 is mounted on a stage 157. In FIG. 6, position-controlunits 158 and 159 correspond to units for controlling a position of alaser beam on an object. The position of the stage 157 is controlled bythe position-control units 158 and 159.

In FIG. 6, the position-control unit 158 controls a position of thestage 157 in the X-direction. The position-control unit 159 controls aposition of the stage 157 in the Y-direction.

The laser irradiating apparatus in FIG. 6 includes the computer 160having a storage unit such as a memory and a central processing unit.The computer 160 controls oscillation by the laser oscillating device151. The computer 160 determines a scanning path of laser light andcontrols the position-control units 158 and 159 such that laser beams oflaser light can be scanned in accordance with the determined scanningpath. Then, the substrate can be moved to a predetermined position.

In FIG. 6, the laser beam position is controlled by moving thesubstrate. However, the laser beam may be moved by using an opticalsystem such as a galvano-meter mirror, or the combination thereof may beused.

In FIG. 6, the computer 160 controls the width of the slit 155 such thata laser beam width can be changed in accordance with the mask patterninformation. The slit is not always necessary.

The laser irradiating apparatus may include a unit for adjusting atemperature of an object. Laser light is light having higher orientationand energy density. Therefore, damper may be provided to preventreflection light from being irradiated to an inappropriate part. Thedamper desirably has a characteristic of absorbing reflection light.Cold water may be circulated within the damper to prevent an increase intemperature of a diaphragm by absorbing reflection light. Furthermore, asubstrate heating unit for heating a substrate may be provided in thestage 157.

In order to form a marker by using laser, a laser oscillating device formarkers may be provided. In this case, the oscillation by the laseroscillating device for markers may be controlled in the computer 160.When the laser oscillating device for markers is provided, an opticalsystem is additionally provided for gathering laser light output fromthe laser oscillating device for markers. Laser used for forming markersmay be YAG laser or CO₂ laser typically. In addition, the other lasermay be used to form markers.

For positioning by using markers, one or several CCD cameras 163 may beprovided. The “CCD camera” refers to a camera using a charge-coupleddevice (CCD) as an imaging element.

Without markers, a pattern on an insulating film or a semiconductor filmmay be identified by using the CCD camera 163 to position the substrate.In this case, mask pattern information of the insulating film or thesemiconductor film, which is input to the computer 160, is compared withactual pattern information of the insulating film or the semiconductorfilm, which is collected by the CCD camera 163. Thus, the substrateposition information can be obtained. In this case, markers are notneeded additionally.

Laser light incident to the substrate is reflected by the surface of thesubstrate and returns to the same optical path as the incident opticalpath (that is, becoming so-called “return light”). The return light hasbad effects such as changes in laser output and/or frequency and/ordestruction of rods. In order to stabilize the laser oscillation byremoving the return light, an isolator may be provided.

FIG. 6 shows the construction of the laser irradiating apparatus havingthe multiple laser oscillating devices. However, a single laseroscillating device may be used. FIG. 7 shows a construction of anotherlaser irradiating apparatus having a single laser oscillating device.The laser irradiating apparatus in FIG. 7 includes a laser oscillatingdevice 201, a chiller 202, an energy density measuring device 215, an AOmodulator 203, an optical system 204, a slit 205 and a CCD camera 213. Asubstrate 206 is placed on the stage 207. The position of the stage 207is controlled by an X-direction position-control unit 208 and anY-direction position-control unit 209. Then, like the one'shown in FIG.6, operations of the components of the laser irradiating apparatus arecontrolled by a computer 210. Unlike the one in FIG. 6, only one laseroscillating device is used. Unlike the case in FIG. 6, the opticalsystem 204 only needs to have a function for gathering one laser lightbeam.

In this way, according to the present invention, after crystallizationby using laser light, a part near edges of each depression or near edgesof each projection in a semiconductor film is removed by patterning.Then, a part having good crystallinity around a center of the depressionis used positively as an active layer of a TFT. Thus, a grain boundarycan be prevented from forming in a channel forming region of the TFT,which can prevent a significant decrease in mobility, a decrease inON-current and/or an increase in OFF current of the TFT due to the grainboundary. The part to be removed near the edge of the depression isdetermined by a designer appropriately.

Laser light does not need to be scanned and be irradiated to an entiresemiconductor film. By scanning laser light such that at least only therequired part can be crystallized, the time can be saved for irradiatinglaser light to a part to be removed by patterning after crystallizingthe semiconductor film. Therefore, processing time taken for onesubstrate can be reduced significantly.

EXAMPLES

Examples of the present invention will be described below.

First Example

A first example is a case where a crystalline semiconductor film isformed on a primary insulating film having grade changes. Then, a TFT isproduced in which a channel forming regions are provided in acrystalline semiconductor film on the projection top portion.

In FIGS. 32A to 32F, a first insulating film 9602, which is a siliconoxide nitride film of 100 nm in thickness, is formed on a glasssubstrate 9601. Then, a silicon nitride film is formed thereon, andsecond insulating films 9603 to 9607 are formed having a rectangularpattern by photo-engraving. The silicon oxide nitride film and thesilicon nitride film are formed by Plasma CVD method.

After an amorphous silicon film 9608 of 150 nm in thickness is formed byPlasma CVD method, a continuous-wave laser beam is irradiated theretofor the crystallization. FIG. 34 is a top view thereof. FIG. 32A is avertical section diagram taken at a line A-A′ in FIG. 34. Areas 9611 to9613 indicated by one-dashed lines over the second insulating films 9603to 9607 are positions where active layers of the TFT are formed.

A linear laser beam 9609 having a uniform energy density distributionlongitudinally is scanned and is irradiated. As a result, as shown inFIG. 32B, a crystalline semiconductor film 9610 is formed. The “uniformenergy density distribution” does not refer to exclusion of those, whichare not completely constant. An acceptable range for the energy densitydistribution is ±5%. The laser beam irradiation may be performed by thelaser processing device having the construction shown in FIGS. 31A and31B. Laser beams gathered by an optical system may have a uniformlongitudinal area in the strength distribution. Laser beams may have atraverse distribution. Crystallization is arranged to have a uniformlongitudinal uniform area in the strength distribution. Thus, an effectfor raising crystal in a direction parallel to the scanning direction ofa laser beam can be improved.

After that, the first insulating film 9602 is etched in a form that acrystalline semiconductor film is left. As a result, active layers 9611to 9613 are formed. FIG. 35 shows a top view of this state.

As shown in FIG. 32D, a gate insulating film 9614 is formed by a siliconoxide film. A conductive film 9615 forming a gate electrode is formed bytungsten or an alloy containing tungsten. Then, as shown in FIG. 32E,gate electrodes 9616 and 9617 are formed by photo-engraving.

Furthermore, a source region and a drain region are formed in each ofthe active layers by doping processing. As a result, a passivation film9618 and a planarization film 9619 are formed. After forming a contacthole, wires 9620 to 9623 are formed on the planarization film 9619 bycombining aluminum, titan and so on appropriately. Thus, an n-channeltype TFT 9630 and a p-channel type TFT 9631, both of which are of thesingle channel type, and an n-channel type TFT 9632 of the multi-channeltype are formed. FIG. 36 shows a top view of this state. FIG. 32F is avertical section diagram taken at a line A-A′ in FIG. 36. FIG. 36 showsan example where the single channel, n-channel type TFT 9630 andp-channel type TFT 9631 form an inverter circuit. FIG. 33 shows avertical section diagram taken at a line B-B′ in FIG. 36.

FIG. 37 shows an equivalent circuit of the single-channel, n-channeltype TFT 9630 and p-channel type TFT 9631 and the multi-channel,n-channel type TFT 9632. The multi-channel, n-channel type TFT 9632forms one transistor by having multiple parallel channels between sourceand drain regions. In this way, by having parallel channel formingregions, a feedback is caused by resistance of the source and drainregions and/or resistance of a low density drain region. Thus, currentsflowing the channels can be leveled out. By using the transistor withthe construction, a variation in characteristic between multipleelements can be reduced.

Second Example

Like the first example, in order to form active layers, a laser beam maybe irradiated to an amorphous semiconductor film for crystallization.However, after poly-crystallization, the laser beam may be furtherirradiated so as to improve the crystallinity. This two-levelcrystallization processing can form a crystalline semiconductor filmhaving fewer distortions than those of the first example.

FIGS. 38A to 38C are vertical section diagrams showing the processingsteps. In FIG. 38A, a first insulating film 9502, which is a siliconoxide nitride film of 100 nm in thickness, is formed on a glasssubstrate 9501. A silicon oxide film is formed thereon, and secondinsulating films 9503 to 9506 are formed having a rectangular pattern byphoto-engraving. Then, an amorphous silicon film 9507 of 150 nm inthickness is formed thereon.

Ni is added to an entire surface of the amorphous semiconductor film9507. Ni is a medium element, which can decrease a temperature forcrystallizing silicon and can improve the orientational characteristic.A method of adding Ni is not limited and may be spin-coating method,vapor-deposition method or sputtering method. In the spin coatingmethod, a solution containing 5 ppm nickel salt acetate is coated on thesurface to form a medium-element containing layer 510. The mediumelement is not limited to Ni and may be the other publicly knownmaterial.

After that, as shown in FIG. 38B, the amorphous silicon film 9507 iscrystallized by heating processing at 580° C. for four hours. As aresult, a crystalline silicon film 511 may be obtained. The crystallinesilicon film 511 is formed by a collection of stick-shaped orneedle-shaped crystal. Each crystal grows in a specific orientation in amacroscopic manner. Therefore, the uniform crystallinity is obtained.Additionally, the orientational rate in a specific direction is high.

As shown in FIG. 38C, a continuous-wave laser beam is irradiated to thecrystalline semiconductor film having crystallized through heatingprocessing so as to improve the crystallinity. The linear laser beam9505 having uniform longitudinal energy density distribution is scannedand is irradiated to the crystal semiconductor film. Thus, thecrystalline semiconductor film 511 is melted and is re-crystallized. Theamorphous area left in the crystalline semiconductor film 511 can bealso crystallized through this processing. This re-crystallizationprocessing can control an increase in grain size and the orientation.During the crystallization stage, a small amount of volume shrinkageoccurs. Then, the distortion is accumulated in grade changes. Thus, acrystalline semiconductor film 512 can be formed without affecting onthe crystalline semiconductor film on the second insulating film.

After that, by following the same steps as those of the first example, aTFT can be completed.

Third Example

In the method of producing a primary insulating film having projectionsand depressions according to the first example, as shown in FIG. 39A, afirst insulating film 9702 formed by a silicon oxide nitride film and asecond insulating film 9703 formed by a silicon nitride film are stackedon a glass substrate 9701. After that, as shown in FIG. 39B, a mask 9704is formed thereon, and the second insulating film 9703 is formed in apattern having areas 9705 to 9708. An example of etching methods may bewet-etching, which can etch with better selectivity by using a mixedsolution containing hydrogen ammonium fluoride (NH₄HF₂) of 7.13% andammonium fluoride (NH₄F) of 15.4%.

In order to form an amorphous semiconductor film thereon, a siliconoxide nitride film 9709 and an amorphous semiconductor film 9710 may beformed continuously in a plasma CVD apparatus without exposing them tothe air. Thus, the contamination effect of the interface with theprimary insulating film can be avoided. Through this processing method,a cleaner interface can be formed. Thus, the occurrence of crystalcores, which cannot be controlled due to the interface impurities, maybe prevented.

After this, by following the same steps as those of the first and secondexamples, a TFI can be completed.

Fourth Example

According to another method of producing a primary insulating filmhaving projections and depressions, as shown in FIG. 40A, a siliconoxide film is formed on the glass substrate 9701. Then, insulating films9711 to 9714 are formed by silicon oxide films by photo-engraving andare formed into rectangular or strip patterns.

Then, after the mask 9710 is removed, a first insulating film 9715 isformed by a silicon oxide nitride film by covering the pattern formed bythe insulating films 9711 to 9714. Then, an amorphous semiconductor film9716 is formed on the first insulating film. The silicon oxide nitridefilm formed as the first insulating film can block, for example, alkalimetal contained in the glass substrate 9701. In addition, the siliconoxide nitride film has lower internal stress. Therefore, the siliconoxide nitride film is suitable for a primary insulating film in contactwith a semiconductor film.

After this, a TFT may be completed by following the same steps of thoseof any one of the first to third examples.

Fifth Example

The present invention can be applied to various semiconductor devices. Aform of a display panel produced based on the first to the fifthexamples will be described with reference to FIGS. 41 and 42.

In FIG. 41, a substrate 9901 includes a pixel portion 9902,gate-signal-side driving circuits 9901 a and 9901 b, a data-signal-sidedriving circuit 9901 c, an input/output terminal portion 9908 and a wireor wires 9904. A shield pattern 9905 may be overlapped partially withthe gate-signal-side driving circuits 9901 a and 9901 b, thedata-signal-side driving circuit 9901 c and the wire or wires 9904,which connect the driving circuits and the input terminal. Thus, a sizeof a frame area of a display panel (that is, peripheral area of thepixel portion) can be reduced. An FPC 9903 is fixed to an external inputterminal portion.

The TFT shown in the first to fifth examples can be applied as aswitching element of the pixel portion 9902, and as active elementsincluded in the gate-signal-side driving circuits 9901 a and 9901 b andthe data-signal-side driving circuit 9901 c.

FIG. 42 is an example of a construction of one pixel of the pixelportion 9902 shown in FIG. 41. The pixel includes TFTs 9801 to 9803.These TFTs are used for switching, resetting and driving in order tocontrol a light-emitting element and/or a liquid crystal elementincluded in the pixel.

Active layers 9812 to 9814 of these TFTs are placed in projection topportion of a primary insulating film therebelow. A crystallinesemiconductor film forming the active layers can be formed based on thefirst to fourth examples. Gate wires 9815 to 9817 are formed on theactive layers 9812 to 9814. Then, a data line 9818, a power-supply line9819, the other different kinds of wires 9820 and 9821 and a pixelelectrode 9823 are formed thereon through a passivation film and aplanarization film.

In this way, according to the present invention, a display panel can becompleted with no effects.

Sixth Example

A semiconductor device including TFTs produced according to the presentinvention can be applied in various ways. For example, the semiconductormay be a mobile information terminal (such as an electrical organizer, amobile computer and a mobile telephone), a video camera, a digitalcamera, a personal computer, a television receiver, a mobile telephoneor a projecting type display apparatus. These examples are shown inFIGS. 43A to 44D.

FIG. 43A is an example of a television receiver completed by applyingthe present invention. The television receiver includes a cabinet 3001,a supporting base 3002 and a display portion 3003. TFTs producedaccording to the present invention are applied to the display portion3003. Therefore, a television receiver can be completed according to thepresent invention.

FIG. 43B is an example of a video camera completed by applying thepresent invention. The video camera includes a body 3011, a displayportion 3012, a voice input portion 3013, an operation switch 3014, abattery 3015 and a receiver 3016. TFTs produced according to the presentinvention are applied to the display portion 3012. Therefore, a videocamera can be completed according to the present invention.

FIG. 43C is an example of a laptop personal computer completed byapplying the present invention. The laptop personal computer includes abody 3021, a cabinet 3022, a display portion 3023 and a keyboard 3024.TFTs produced according to the present invention are applied to thedisplay portion 3023. Therefore, a personal computer can be completedaccording to the present invention.

FIG. 43D is an example of a personal digital assistant (PDA) completedby applying the present invention. The PDA includes a body 3031, astylus 3032, a display portion 3033, an operation button 3034 and anexternal interface 3035. TFTs produced according to the presentinvention are applied to the display portion 3033. Therefore, a PDA canbe completed according to the present invention.

FIG. 43E is an example of a sound-effect playing apparatus by applyingthe present invention. Specifically, the sound-effect playing apparatusis a car-mounted audio apparatus and includes a body 3041, a displayportion 3042 and operation switches 3042 and 3044. TFTs producedaccording to the present invention are applied to the display portion3042. Therefore, an audio apparatus can be completed according to thepresent invention.

FIG. 43F is an example of a digital camera completed by applying thepresent invention. The digital camera includes a body 3051, a displayportion (A) 3052, an objective portion 3053, an operation switch 3054, adisplay portion (B) 3055 and a battery 3056. TFTs produced according tothe present invention are applied to the display portion (A) 3052 andthe display portion (B) 3055. Therefore, a digital camera can becompleted according to the present invention.

FIG. 43G is an example of a mobile telephone completed by applying thepresent invention. The mobile telephone includes a body 3061, a voiceoutput portion 3062, a voice input portion 3063, a display portion 3064,an operation switch 3065 and an antenna 3066. TFTs produced according tothe present invention are applied to the display portion 3064.Therefore, a mobile telephone can be completed according to the presentinvention.

FIG. 44A is a front type projector and includes a projecting apparatus2601 and a screen 2602. FIG. 44B is a rear type projector and includes abody 2701, a projecting apparatus 2702, a mirror 2703 and a screen 2704.

FIG. 44C shows an example of a construction of the projecting apparatus2601 and 2702 in FIGS. 44A and 44B. Each of the projecting apparatus2601 and 2702 includes a light source optical system 2801, mirrors 2802and 2804 to 2806, a dichroic mirror 2803, a prism 2807, a liquid crystaldisplay apparatus 2808, a phase contrast place 2809 and a projectingoptical system 2810. The projecting optical system 2810 includes anoptical system having a projecting lens. This example shows an apparatusof a three-plate type but is not limited thereto. For example, theapparatus may be of a single-plate type. In addition, an optical systemmay be provided, by a practitioner appropriately, in an optical pathindicated by an arrow in FIG. 44C, such as an optical lens, a filmhaving a polarizing function, a film for adjusting a phase differenceand an IR film.

FIG. 44D shows an example of a construction of the light source opticalsystem 2801 in FIG. 44C. In this example, the light source opticalsystem 2801 includes a reflector 2811, a light source 2812, lens arrays2813 and 2814, a polarization converting element 2815, and alight-gathering lens 2816. The light source optical system shown in FIG.44D is only the example and is not especially limited. For example, anoptical system may be provided, by a practitioner appropriately, with anoptical system such as an optical lens, a film having a polarizingfunction, a film for adjusting a phase difference and an IR film.

These apparatus shown herein are only the part of examples. The presentinvention is not limited to these applications.

Seventh Example

A method for forming an insulating film having depressions andprojections will be described in this example.

First of all, as shown in FIG. 8A, a first insulating film 251 is formedof a substrate 250. In this example, the first insulating film 251 isformed on silicon oxide nitride but is not limited thereto. The firstinsulating film 251 only needs to have a more select rate for etchingthan that of a second insulating film. In this example, the firstinsulating film 251 is formed of 50 to 200 nm in thickness by using SiH₄and N₂O in a CVD apparatus. The first insulating film may be a singlelayer or may have a structure depositing multiple insulating films.

Next, as shown in FIG. 8B, a second insulating film 252 is formed suchthat the second insulating film 252 can be in contact with the firstinsulating film 251. The second insulating film 252 is patterned to formdepressions and projections in a later step. In this case, the secondinsulating film 252 needs to have a thickness, which allows depressionsand projections to appear on the surface of a semiconductor film formedlater. In this example, as the second insulating film 252, silicon oxideis formed of 30 to 300 nm in thickness by using Plasma CVD method.

Next, as shown in FIG. 8C, a mask 253 is formed. Then, the secondinsulating film 252 is etched. In this example, the wet-etching isperformed at 20° C. by using a mixed solution containing ammoniumbifluoride (NH₄HF₂) of 7.13% and ammonium fluoride (NH₄F) of 15.4% (forexample, LAL 500 (product name) of Stella Chemifa Corporation) as anetchant. Through this etching, rectangular or stripe-shaped projections254 are formed. The first insulating film 251 and the projection 253 areregarded as one insulating film herein.

Next, a semiconductor film is formed so as to cover the first insulatingfilm 251 and the projections 253. In this example, the thickness of theprojection is 30 nm to 300 nm. Therefore, the thickness of thesemiconductor film is desirably 50 to 200 nm. In this case, thethickness of the semiconductor is 60 nm. When an impurity is presentbetween the semiconductor film and the insulating film, thecrystallinity of the semiconductor is adversely effected. Then, avariation in characteristic and/or changes in threshold voltage of a TFTto be produced may increase. Therefore, the insulating film and thesemiconductor film are desirably formed continuously. In this example,after the insulating film including the first insulating film 251 andthe projections 253 is formed, a silicon oxide film 255 is formed thinlyon the insulating film. Then, in order to prevent it from being exposedto the air, a semiconductor film 256 is formed continuously. A designercan define the thickness of the silicon oxide film appropriately. Inthis example, the thickness of the silicon oxide film is 5 nm to 30 nm.

The second insulating film 252 may be etched such that the projectionscan be tapered. By having tapered projections, a semiconductor film, agate insulting film, a gate electrode and so on to be formed on theinsulating film may be prevented from being damaged by the edges of theprojections.

Next, another method of forming an insulating film will be describedwhich is different from the one shown in FIGS. 8A to 8D. First of all,as shown in FIG. 9A, a first insulating film is formed on a substrate260. The first insulating film may be a silicon oxide film, a siliconnitride film, a silicon oxide nitride film or the like.

When a silicon oxide film is used, according to Plasma CVD method,tetraethyl orthosilicate (TEOS) and O₂ are mixed and are discharged byhaving the reaction pressure of 40 Pa, the substrate temperature of 300°C. to 400° C. and the high frequency (13.56 MHz) power density of 0.5 to0.8 W/cm². The silicon oxide nitride film to be used as the firstinsulating film may be a silicon oxide nitride film produced from SiH₄,N₂O and NH₃ or a silicon oxide nitride film produced from SiH₄ and N₂O,according to Plasma CVD method. In this case, the producing conditionincludes the reaction pressure of 20 to 200 Pa, the substratetemperature of 300 to 400° C. and the high frequency (60 MHz) powerdensity of 0.1 to 1.0 W/cm². Alternatively, a silicon oxide nitridehydride film produced from SiH₄, N₂O and H₂ may be applied. Like thesilicon nitride film, the silicon oxide nitride hydride film may beproduced from SiH₄ and NH₃ by using Plasma CVD method.

The first insulating film is formed of 20 to 200 nm (preferably 30 to 60nm) in thickness on the entire surface of the substrate. Then, as shownin FIG. 9B, a mask 262 is formed by using a photolithography technology.Unnecessary parts are removed by etching, and stripe-shaped orrectangular projections 263 are formed. For the first insulating film261, a dry-etching method using fluorine gas or a wet-etching methodusing a fluorine solution may be used. If the wet-etching method isused, a mixed solution containing ammonium bifluoride (NH₄HF₂) of 7.13%and ammonium fluoride (NH₄F) of 15.4% (for example, LAL 500 (productname) of Stella Chemifa Corporation) may be used for the etching.

Next, a second insulating film 264 is formed by covering projections 262and the substrate 260. This layer may be a silicon oxide film, siliconnitride film or a silicon oxide and nitride film, like the firstinsulating film 261, of 50 to 300 nm (preferably, 100 to 200 nm) inthickness.

Through the production steps, an insulating film including theprojections 262 and the second insulating film 264 is formed. After thesecond insulating film 264 is formed, a semiconductor film is formedcontinuously in order to prevent the second insulating film 264 frombeing exposed to the air. Thus, impurities in the air are prevented fromintruding between the semiconductor film and the insulating film.

Eighth Example

In this example, a semiconductor film formed on a stripe-shapedinsulating film is crystallized by laser light irradiation. Then,islands separated from each other are formed on depression surfacesparallel to the substrate. Then, a TFT is produced by using the islands.This example will be described below.

FIG. 10A shows a construction of a TFT according to this example. InFIG. 10A, an insulating film 152 having stripe-shaped projections 151 isformed on a substrate 150. Multiple islands 153 separated from eachother are formed on the top surface of each depression between theprojections 151. A gate insulating film 154 is formed so as to be incontact with the island 153. The gate insulating film 154 shown in FIG.10A is formed such that an impurity area of the island can be exposed.However, the gate insulating film may be formed by covering the island153.

Multiple gate electrodes 155 are formed on the gate insulating film 154by overlapping with multiple islands 153. The multiple gate electrodes153 may be connected to each other in some circuit constructions.

FIG. 10B shows a section diagram taken at a line A-A′ in FIG. 10A. FIG.10C shows a section diagram taken at a line B-B′ in FIG. 10A. As shownin FIG. 10C, each of the gate electrodes 155 is overlapped with achannel forming region 156 of the island 153 through the gate insulatingfilm 154. The channel forming region 156 is also between two impurityregions 157 included in the island 153.

This example can be implemented in combination with the first to seventhexamples.

Ninth Example

This example will be described about various forms of an insulatingfilm.

FIG. 11A shows an example of the form of an insulating film according tothe present invention. In FIG. 11A, an insulating film 171 is formed ona substrate 170. The insulating film 171 has multiple projections 172.Each of the projections is rectangular when viewed from the above. Allof the projections have a longer side direction or shorter sidedirection of the rectangular, which is parallel to a scanning directionof laser light indicated by an arrow.

The projection 172 does not always have the same widths in the scanningdirection of laser light and in the direction perpendicular to thescanning direction. A form of insulating film is desirably designed inaccordance with a desired form of an island.

FIG. 11B shows another example of the form of the insulating filmaccording to the present invention. In FIG. 11B, an insulating film 181is formed on a substrate 180. The insulating film 181 has a rectangularprojection 182 each having slit-shaped opening portions when viewed fromthe above. A longer or shorter side direction of the slit of theprojection 182 is parallel with a scanning direction of laser lightindicated by an arrow.

Next, an example of a construction of a TFT will be described which isformed by using an insulating film having slit-shaped opening portionsshown in FIG. 11B.

FIG. 12A shows a top view of the TFT according to this example. As shownin FIG. 12A, in this example, an insulating film is used which has arectangular projection 160 having slit-shaped opening portions inside. Asemiconductor film is formed by covering the projection 160. Laser lightscans in a direction indicated by an arrow along a direction of a majoraxis of the slit-shaped opening portion. Thus, the semiconductor film iscrystallized. Then, the semiconductor film is patterned, and an island161 having opening portions is formed. A channel forming region isformed on the top surface of a depression surrounded by projections.

Then, a gate insulating film 162 is formed so as to be in contact withthe island 161. FIG. 12B is a section diagram taken at a line A-A′ inFIG. 12A. FIG. 12C is a section diagram taken at a line B-B′. FIG. 12Dis a section diagram taken at a line C-C′.

A conductive film is formed on the gate insulating film 162. Theconductive film is patterned so that a gate electrode 163 can be formed.The gate electrode 163 overlaps with a channel forming region 164 of theisland 161 through the gate insulating film 162. The channel formingregion 164 is between two impurity regions 165 included in the island161.

A first interlayer insulating film 166 is formed so as to cover the gateelectrode 163, the island 161 and the gate insulating film 162. Thefirst interlayer insulating film 166 is an inorganic insulating film andcan prevent a substance adversely affecting on characteristics of TFT ofalkali metal from intruding into the island 161.

Then, a second interlayer insulating film 167 of organic resin is formedon the first interlayer insulating film 166. The second interlayerinsulating film 167, the first interlayer insulating film 166 and thegate insulating film 162 have opening portions formed by etching. Wires168 and 169 are formed on the second interlayer insulating film 167. Thewires 168 and 169 are connected to two impurity areas 165 and the gateelectrode 163, respectively, through the opening portions.

In this example, the multiple channel forming regions 164 are formed. Inaddition, the multiple channel forming regions 164 are separated fromeach other. Therefore, by increasing a channel width of each of thechannel forming regions, ON current can be obtained. At the same time,heat generated by driving TFTs can be released efficiently.

This example can be implemented in combination with the first to eighthexamples.

Tenth Example

This example is a method of producing an active matrix substrate byusing a laser crystallization method according to the present invention.This example will be described with reference to FIGS. 13A to 16. Forconvenience, an active matrix substrate refers to a substrate having aCMOS circuit, a driving circuit, and a pixel portion having pixel TFTsand a latching capacity thereon.

First of all, a substrate 600 of glass such as barium borosilicate glassor aluminosilicate glass is used. The substrate 600 may be obtained byforming an insulating film on a substrate of a quartz substrate, siliconsubstrate, a metal substrate or a stainless substrate. Alternatively, aplastic substrate may be used which has heat resistance resisting aprocessing temperature of this example.

Next, an insulating film of 100 to 300 nm in thickness such as a siliconoxide film, a silicon nitride film and a silicon oxide nitride film isformed on the substrate 600 by using a publicly known method (such asSputtering method, LPCVD method and Plasma CVD method).

Next, in order to form thick parts and thin parts in the insulating filmaccording to this example, a mask 693 of resist is formed byphoto-engraving (photolithography), and etching processing is performedthereon. The thickness depends on the etching amounts. In this example,the thickness is about 50 to 100 nm. For example, in order to etch asilicon oxide nitride film of 150 nm in thickness by 75 nm, wet-etchingusing a solution containing fluoride may be used. Alternatively,dry-etching using CF₄ may be applied. In this way, an insulating film601 having projections is formed. Here, a width of the projection in adirection perpendicular to the scanning direction of laser light may bedetermined properly in consideration of a size of a TFT to be produced.A size (diameter or a length of a diagonal line) as much as 2 to 6 μm ispreferable in order to control a number of created crystal cores (FIG.13A).

Next, an amorphous semiconductor film 692 of 25 to 80 nm in thickness(preferably, 30 to 60 nm in thickness) is formed on the insulating film601 by using a publicly known method (such as Sputtering method, LPCVDmethod and Plasma CVD method) (FIG. 13B). In this example, an amorphoussemiconductor film is formed but may be a microcrystal semiconductorfilm or a crystalline semiconductor film. Alternatively, a compoundsemiconductor film may be formed having an amorphous structure such asan amorphous silicon geranium film.

Next, the amorphous semiconductor film 692 is crystallized by lasercrystallizing method. The scanning direction of the laser light isarranged to be parallel with a direction that the stripe-shapedprojections extend in the insulating film 601. If the projection in theinsulating film 601 is rectangular when viewed from the above of thesubstrate, the scanning direction of the laser light is determined so asto be parallel with a direction of the longer or shorter side of therectangle. More specifically, based on mask information input to acomputer of the laser irradiating apparatus, laser light is irradiatedselectively. In this case, the crystallization may be implemented notonly by the laser crystallization method but also in combination withthe other publicly known crystallization method (such as a thermalcrystallization method using RTA and/or furnace annealing and a thermalcrystallization method using a metal element promoting thecrystallization). In this example, a width of a laser beam is changed byusing a slit in accordance with the width of the insulating film in adirection perpendicular to the scanning direction. However, the presentinvention is not limited thereto. The slit is not always necessary.

For the crystallizing an amorphous semiconductor film, solid laserprovided for continuous waves may be used, and the second to fourthharmonic waves of a fundamental wave may be used. Thus, large crystalgrains can be obtained. Typically, the second harmonic (532 nm) and/orthe third harmonic wave (355 nm) of Nd:YVO₄ laser (fundamental wave of1064 nm) are desirably used. More specifically, laser light emitted fromthe continuous wave YVO₄ laser is converted to harmonics by a nonlinearoptical element. Thus, laser light has an output of 10 W. Alternatively,YVO₄ crystal and a nonlinear optical element may be put into a resonatorto emit harmonics. Preferably, rectangular or oval laser light is formedon an irradiated surface by an optical system and is irradiated to anobject. The energy density here must be about 0.01 to 100 MW/cm²(preferably, 0.1 to 10 MW/cm²). The laser light is irradiated at a speedof about 10 to 2000 cm/s by moving the semiconductor film relatively.

For the laser irradiation, pulse or continuous wave gaseous laser orsolid laser may be used. The gaseous laser may be excimer laser, Arlaser, Kr laser or the like. The solid laser may be YAG laser, YVO₄laser, YLF laser, YAO₃ laser, glass laser, ruby laser, alexandritelaser, Ti:sapphire laser, Y₂O₃ laser or the like. The solid laser may belaser using crystal such as YAG, YVO₄, YLF and YAO₃ to which Cr, Nd, Er,Ho, Ce, Co, Ti, Yb or Tm is doped. Alternatively, slab laser may beused. A fundamental wave of the laser depends on the material to bedoped. Laser light having a fundamental wave of around 1 μm can beobtained. A harmonic for the fundamental wave can be obtained by using anon-linear optical element.

As a result of the laser crystallization, a crystalline semiconductorfilm 694 having improved crystallinity is formed (FIG. 13C). In thecrystalline semiconductor film, a grain boundary may occur easily nearthe edges of projections or depressions.

Next, the crystalline semiconductor film 694 having improvedcrystallinity is patterned into a desired form. Thus, crystallizedislands 602 to 606 are formed (FIG. 13D).

After the islands 602 to 606 are formed, a slight amount of impurityelement (boron or phosphorous)may be doped in order to control thethreshold value of a TFT.

Next, a gate insulating film 607 covering the islands 602 to 606 isformed. The gate insulating film 607 contains silicon and is formed of40 to 150 nm in thickness by using Plasma CVD method or Sputteringmethod. In this example, a silicon oxide nitride film of 110 nm inthickness (composition rate: Si=32%, O=59%, N=7% and H=2%) is formed byPlasma CVD method. The gate insulating film is not limited to thesilicon oxide nitride film and may be the other insulating filmcontaining silicon having a single-layer or laminated structure.

When a silicon oxide film is used, according to Plasma CVD method,tetraethyl orthosilicate (TEOS) and O₂ are mixed and are discharged byhaving the reaction pressure of 40 Pa, the substrate temperature of 300°C. to 400° C. and the high frequency (13.56 MHz) power density of 0.5 to0.8 W/cm². The produced silicon oxide film can obtain goodcharacteristics as a gate insulating film by later thermal annealing at400° C. to 500° C.

Next, a first conductive film 608 of 20 to 100 nm in thickness and asecond conductive film 609 of 100 to 400 nm in thickness are stacked onthe gate insulating film 607 (FIG. 14A). In this example, the firstconductive film 608 containing a TaN film of 30 nm in thickness and thesecond conductive film 609 containing a W film of 370 nm in thicknessare stacked. The TaN film is formed by Sputtering method. Ta is used asa target and is sputtered in an atmosphere containing nitrogen. The Wfilm is formed by Sputtering method using W as a target. Alternatively,a thermal CVD method may be used by using tungsten hexafluoride (WF₆).In all of the cases, in order to use them as gate electrodes, theresistance must be reduced. Therefore, the resistance of the W film isdesirably not more than 20 μm. The resistance of the W film can bereduced by increasing the grain size. However, when the W film containsmany impurity elements such as oxygen, the crystallization is disturbed.Then, the resistance is increased. Therefore, in this example, the Wfilm is formed by using Sputtering method using high purity W (purity of99.9999%) as a target and by preventing impurities from the vapor phasefrom intruding into the W film. As a result, the resistance of 9 to 20μm can be achieved.

In this example, the first conductive film 608 and the second conductivefilm 609 are TaN and W, respectively, but are not limited thereto. Eachof them may -be formed by an element selected from Ta, W, Ti, Mo, Al,Cu, Cr and Nd, or an alloy or compound material mainly containing theelement. Alternatively, a semiconductor such as a polycrystallinesilicon film to which an impurity element such as phosphorus is dopedmay be used. An AgPdCu alloy may be used. Combinations of a tantalum(Ta) film as the first conductive film and a W film as the secondconductive film, a titan nitride (TiN) film as the first conductive filmand a W film as the second conductive film, and the first conductivefilm of tantalum nitride (TaN) and the second conductive film of W arepossible. Alternatively, combinations of a tantalum nitride (TaN) as thefirst conductive film and an Al film as the second conductive film, anda tantalum nitride (TaN) film as the first conductive film and a Cu filmas the second conductive film are possible.

This example is not limited to the two-layered structure but may be athree-layered structure sequentially stacking a tungsten film, analuminum-silicon (Al—Si) alloy film and a titan nitride film, forexample. In the three-layered structure, tungsten nitride may be usedinstead of tungsten. Aluminum-titan (Al—Ti) alloy film may be usedinstead of the aluminum-silicon (Al—Si) alloy film. A titan film may beused instead of the titan nitride film.

Importantly, the best-suitable etching method and etchant type areselected properly in accordance with the materials of the conductivefilms.

Next, masks 610 to 615 of resist are formed by using photolithographymethod. Then, first etching processing is performed for formingelectrodes and wires. The first etching processing is performed underthe first and second etching conditions (FIG. 14B). In this example, asthe first etching condition, Inductively Coupled Plasma (ICP) etchingmethod is used. CF₄, Cl₂ and O₂ are used as etching gas. The gas flowrate is 25:25:10 (sccm), respectively. Plasma is generated by supplyingRF (13.56 MHz) power of 500 W to a coil type electrode at a pressure of1 Pa. Then, etching is performed. RF (13.56 MHz) power of 150 W is alsosupplied to the substrate side (sample stage). Essentially negativeself-bias voltage is applied. Under the first etching condition, the Wfilm is etched, and the end of the first conductive layer is tapered.

Then, the first etching condition is replaced by the second etchingcondition without removing the masks 610 to 615 of resist. CF₄ and Cl₂are used as etching gas. The gas flow rate is 30:30 (sccm),respectively. Plasma is generated by supplying RF (13.56 MHz) power of500 W to a coil type electrode at a pressure of 1 Pa. Then, etching isperformed for about 30 seconds. RF (13.56 MHz) power of 20 W is alsosupplied to the substrate side (sample stage). Essentially negativeself-bias voltage is applied. Under the second etching condition mixingCF₄ and C₁₂, the W film and the TaN film are etched to the same extent.In order to perform etching without leaving residues, the etching timemay be increased by 10% to 20%.

The masks of resist in the suitable form are used for the first etchingprocessing. Thus, the ends of the first conductive layer and secondconductive layer can be tapered because of the effect of the biasvoltage applied to the substrate side. The angle of the tapered part is15° to 45°. In this way, by performing the first etching processing,conductive layers 617 to 622 (first conductive layers 617 a to 622 a andsecond conductive layers 617 b to 622 b) can be formed in the first formincluding the first conductive layer and the second conductive layer.FIG. 14B includes a gate insulating film 616. Areas not covered by theconductive layers 617 to 622 in the first form are. etched and becomethin.

Next, second etching processing is performed without removing masks ofresist (FIG. 14C). Here, CF₄, Cl₂ and O₂ are used as etching gas, andthe W film is etched selectively. In this case, the second conductivelayers 628 b to 633 b are formed by the second etching processing. Onthe other hand, the first conductive layers 617 a to 622 a are notetched very much. Then, conductive layers 628 to 633 in a second formare formed.

Then, first doping processing is performed without removing the masks ofresist, and an impurity element giving the n-type is added to the islandin low density. The doping processing may be performed according toion-doping method or ion-implantation method. The ion-doping method isperformed under a condition having the dose amount of 1×10¹³ to 5×10¹⁴atoms/cm² and the accelerating voltage of 40 to 80 kV. In this example,the dose amount is 5×10¹³ atoms/cm², and the accelerating voltage is 60kV The impurity element giving n-type is an element belonging to group15 element and typically may be phosphorous (P) or arsenic (As). In thisexample, phosphorus (P) is used. Here, the conductive layers 628 to 633are masks against the impurity element giving n-type. Impurity areas 623to 627 are formed in a self-alignment manner. The impurity elementgiving n-type is added to the impurity areas 623 to 627 in the densityrange of 1×10¹⁸ to 1×10²⁰/cm³.

After removing the masks of resist, masks 634 a to 634 c of resist areformed thereon newly. Then, the second doping processing is performedwith a higher accelerating voltage than that used for the first dopingprocessing. The ion-doping method is performed under a condition havingthe dose amount of 1×10¹³ to 1×10¹⁵ atoms/cm² and the acceleratingvoltage of 60 to 120 kV. In this doping processing, the secondconductive layers 628 b to 632 b are used as masks against an impurityelement. Then, doping is performed such that the impurity element isadded to the lower island of the tapered part of the first conductivelayer. Then, third doping processing is performed with a loweraccelerating voltage than that of the second doping processing. As aresult, a state shown in FIG. 15A is obtained. The ion-doping method isperformed under a condition having the dose amount of 1×10¹⁵ to 1×10¹⁷atoms/cm² and the accelerating voltage of 50 to 100 kV. By performingthe second doping processing and the third doping processing, theimpurity element giving n-type is added in a density range of 1×10¹⁸ to5×10¹⁹/cm³ to low-density impurity areas 636, 642 and 648 overlappingwith the first conductive layer. The impurity element giving n-type isadded in a density range of 1×10¹⁹ to 5×10²¹/cm³ to high-densityimpurity areas 635, 638, 641, 644 and 647.

By using a proper accelerating voltage, the second doping processing andthe third doping processing can form the low-density impurity area andthe high-density impurity area one time.

Next, after the masks of resist are removed, masks 650 a to 650 c ofresist are formed newly, and fourth doping processing is performed. Byperforming the fourth doping processing, impurity areas 653, 654, 659and 660 are formed on islands, which is active layers of p-channel-typeTFTs. The impurity areas 653, 654, 659 and 660 contains an impurityelement giving the other conductive type opposite against the oneconductive type. The second conductive layers 628 a to 632 a are used asmasks against the impurity element. Then, by adding the impurity elementgiving p-type, the impurity areas are formed in a self-alignment manner.In this example, the impurity areas 653, 654, 659 and 660 are formed byion-doping method using diborane (B₂H₆) (FIG. 15B). During the fourthdoping processing, the islands on which n-channel-type TFFs are formedare covered by the masks 650 a to 650 c of resist. Through the first tothird doping processing, phosphorous of different densities is added tothe impurity areas 653 and 654 and 659 and 660. However, dopingprocessing is performed on all of the areas such that the density of theimpurity element giving p-type can be 1×10¹⁹ to 5×10²atoms/cm³. Thus, noproblems occur when these areas function as source regions and drainregions of p-channel-type TFTs.

Through these steps, impurity areas are formed on the islands.

Next, the masks 650 a to 650 c of resist are removed, and a firstinterlayer insulating film 661 is formed. As the first interlayerinsulating film 661, an insulating film containing silicon of 100 to 200nm in thickness is formed by using Plasma CVD method or Sputteringmethod. In this example, a silicon oxide nitride film of 150 nm inthickness is formed by Plasma CVD method. However, the first interlayerinsulating film 661 is not limited to the silicon oxide nitride film butmay be the other insulating layer containing silicon in a single-layeror laminated structure.

Next, as shown in FIG. 15C, a laser irradiating method is used asactivation processing. If laser-annealing method is used, laser havingused for crystallization may be used. The activation requires laser atthe same moving speed as that for the crystallization with an energydensity of about 0.01 to 100 MW/cm² (preferably, 0.01 to 10 MW/cm²).Continuous wave laser may be used for the crystallization while pulselaser may be used for the activation.

The activation processing may be performed before the first interlayerinsulating film is formed.

With heating processing (thermal processing at 300° C. to 550° C. forone to 12 hours), hydrogenation can be performed. This processingterminates dangling bonds of the islands by using hydrogen contained inthe first interlayer insulating film 661. As the other methods for thehydrogenation, plasma hydrogenation (using hydrogen excited by plasma)or heating processing at 300° C. to 650° C. for one to 12 hours in anatmosphere containing 3% to 100% of hydrogen may be performed. In thiscase, the semiconductor layer can be hydrogenated independently of theexistence of the first interlayer insulating film.

Next, a second interlayer insulating film 662 is formed on the firstinterlayer insulating film 661 by using an inorganic insulating filmmaterial or an organic insulator material. In this example, an acrylresin film of 1.6 μm in thickness is formed. Next, after the secondinterlayer insulating film 662 is formed, a third interlayer insulatingfilm 672 is formed in contact with the second interlayer insulating film662. In this example, a silicon nitride film is used as the thirdinsulating film 672.

Then, wires 664 to 668 are formed in a driving circuit 686 forconnecting to the impurity areas electrically. These wires are formed bypatterning a laminated film containing a Ti film of 50 nm in thicknessand an alloy film (of Al and Ti) of 500 nm in thickness. The structureof each of the wires is not limited to the two-layered structure but maybe a single layer structure or a laminate structure having three or morelayers. The materials for the wires are not limited to Al and Ti. Forexample, Al and Cu may be formed on a TaN film, and then a Ti film maybe formed thereon in order to obtain a laminated film. The laminatedfilm may be patterned to form wires (FIG. 16).

In a pixel portion 687, a pixel electrode 670, a gate wire 669 and aconnecting electrode 668 are formed. The connecting electrode 668electrically connects a source wire (a laminated layer of 643 a and 643b) to a pixel TFT. The gate wire 669 electrically connects to a gateelectrode of the pixel TFT. The pixel electrode 670 electricallyconnects to a drain region 690 of the pixel TFT. Furthermore, the pixelelectrode 670 electrically connects to an island 685 functioning as oneelectrode forming a latching capacity. The pixel electrode and theconnecting electrode are formed by using the same material herein.However, for the pixel electrode 670, a material having goodreflectivity against a film mainly containing Al or Ag or a laminatedfilm thereof is desirably used.

In this way, the CMOS circuit having the n-channel type TFT 681 and thep-channel type TFT 682, the driving circuit 686 having the n-channeltype TFT 683, the pixel TFT 684, and the pixel portion 687 having thelatching capacity 685 can be formed on the same substrate. As a result,the active matrix substrate is completed.

The n-channel type TFT 681 of the driving circuit 686 has a channelforming region 637, a low-density impurity region 636 overlapping withthe first conductive layer 628 a forming a part of the gate electrode(Gate Overlapped LDD (GOLD) region) and high-density impurity region 652functioning as a source region or a drain region. The p-channel type TFT682 forming the CMOS circuit by connecting the n-channel type TFT 681and an electrode 666 has a channel forming region 640, a high-densityimpurity region 653 functioning as a source region or a drain region,and an impurity region 654 containing an impurity element giving p-type.The n-channel type Fi 683 has a channel forming region 643, alow-density impurity region 642 (GOLD region) overlapping with the firstconductive layer 630 a forming a part of a gate electrode, and ahigh-density impurity region 656 functioning as a source region or adrain region.

The pixel TFT 684 of the pixel portion has a channel forming region 646,a low-density impurity region 645 formed outside of a gate electrode(LDD region), and a high-density impurity region 658 functioning as asource region or a drain region. The island functioning as one electrodeof the latching capacity 685 contains an impurity element giving n-typeand an impurity element giving p-type. The latching capacity 685includes an electrode (a laminate layer of 632 a and 632 b) and anisland by using the insulating film 616 as a dielectric.

In the pixel construction according to this example, the end of thepixel electrode and the source wire are arranged to overlap so as toblock light in a gap between pixel electrodes without using a blackmatrix.

In this example, the construction of the active matrix substrate to beused for a liquid crystal display apparatus is described. However, alight-emitting apparatus can be used by using the production stepsaccording to this example. A light-emitting apparatus is generally adisplay panel in which light-emitting elements over a substrate areenclosed between the substrate and a cover or a display moduleimplementing TFTs in the display panel. Each of the light-emittingelements has a layer (light-emitting layer) including an organiccompound, which can obtain electro luminescence generated in an electricfield, an anode layer and a cathode layer.

In the light-emitting element used in this example, a positive-holeimplanting layer, electron implanting layer, positive-hole transportlayer or an electron transport layer can be formed by using an inorganiccompound only or a material containing an inorganic compound mixed withan organic compound. These layers may be mixed partially with eachother.

This example can be implemented in combination with the first to ninthexamples.

Eleventh Example

In this example, in order to crystallize a semiconductor film, a processfor irradiating laser light and a process for crystallizing asemiconductor film by using a medium are combined. When a medium elementis used, the technology disclosed in JP Laid-Open 7-130652 and JPLaid-Open 8-78329 are desirably used.

First of all, as shown in FIG. 17A, an insulating film havingprojections 502 is formed on a substrate 500. Then, a semiconductor film503 is formed on the insulating film 501.

Next, the semiconductor film 503 is crystallized by using a mediumelement (FIG. 17B). For example, when the technology disclosed in the JPLaid-Open 7-130652 is used, a solution containing 10 ppm (in weight)nickel salt acetate is coated to the semiconductor film 503 to form anickel containing layer 504. Then, the nickel containing layer 504undergoes dehydrogenation processing at 500° C. for one hour and thenundergoes thermal processing at 500° C. to 650° C. for 4 to 12 hours, inthis example, at 550° C. for 8 hours. As a result, a semiconductor film505 having improved crystallinity is formed. In addition to nickel (Ni),elements such as germanium (Ge), iron (Fe), palladium (Pd), tin (Sn),lead (Pb), cobalt (Co), platinum (Pt), copper (Cu),. and gold (Au) maybe used as the medium element.

Then, a semiconductor film 506 having further improved crystallinity isformed from the semiconductor film 505 crystallized by NiSPC throughlaser light irradiation. The semiconductor film 506 obtained through thelaser light irradiation includes the medium element. Therefore,processing (gettering) is performed for removing the medium element fromthe semiconductor film 506. The gettering is performed by using thetechnology disclosed in JP Laid-Open 10-135468 or JP Laid-Open10-135469.

More specifically, an area 507 containing phosphorus partially is formedin the semiconductor film 506 obtained after the laser irradiation.Then, the area 507 undergoes thermal processing in an atmosphere ofnitrogen at 550 to 800° C. for 5 to 24 hours, in this case, at 600° C.for 12 hours. Then, the area 507 containing phosphorus of thesemiconductor film 506 works as a gettering site. Then, the mediumelement in the semiconductor film 506 can be segregated to the area 507containing phosphorus (FIG. 17D).

After that, the area 507 containing phosphorus of the semiconductor film506 is patterned to remove. Then, an island 508 can be obtained in whichthe density of the medium element is reduced to not more than1×10¹⁷atoms/cm³, preferably to about 1×10¹⁶atoms/cm³ (FIG. 17E).

After coating a solution containing a medium element to a semiconductorfilm before crystallization, the crystal may be raised by laser lightirradiation instead of SPC.

This example may be implemented in combination with examples 1 to 11.

Twelfth Example

In this example, a form of a laser beam combined by overlapping multiplelaser beams will be described.

FIG. 18A shows an example of a laser beam form of laser lightoscillated, without a slit, from multiple laser oscillating devices onan object. A laser beam shown in FIG. 18A has an oval form. According tothe present invention, a form of a laser beam of laser light oscillatedfrom the laser oscillating device is not limited to the oval form. Theform of the laser beam depends on the type of laser and can be formed byan optical system. For example, a form of laser light emitted from XeClexcimer laser L3308 (with wavelength of 308 mn and pulse width of 30 mn)of Lambda is rectangular of 10 mm×30 mm (half width in beam profile). Aform of laser light emitted from YAG laser is cylindrical or circle inrod form. A form of laser light emitted from slab type laser isrectangular. By forming laser light by using an optical system, laserlight in desired size can be generated.

FIG. 18B shows a distribution of energy densities of laser light in amajor-axis L direction of the laser beam shown in FIG. 18A. The laserbeam shown in FIG. 18A corresponds to an area satisfying an energydensity of equal to ½ of a peak value of the energy density in FIG. 18B.In the distribution, the energy densities of laser light having an ovallaser beam becomes higher toward the center O of the oval. The laserbeam shown in FIG. 18A has an energy density in the center axisdirection following the Gaussian distribution. An area possibly having auniform energy density is small.

Next, FIG. 18C shows a laser beam form resulting from combining laserlight having the laser beam shown in FIG. 18A. FIG. 18C shows a casewhere four laser light laser beams are overlapped to form one linearlaser beam. The number of laser beams to be overlapped is not limitedthereto.

As shown in FIG. 18C, all laser light laser beams have the same majoraxis of the ovals. The laser beams are overlapped and are combinedpartially with each other. As a result, one laser beam 360 is formed. Astraight line obtained by connecting the centers O of all of the ovalsis a center axis of the laser beam 360.

FIG. 18D shows a distribution of energy densities of the combined laserbeam of laser light shown in FIG. 18C in a center axis y direction. Thelaser beam shown in FIG. 18C corresponds to an area satisfying an energydensity equal to ½ of a peak value of the energy density in FIG. 18B. Ina part all of the laser beams before combined, energy densities areadded. For example, when energy densities L1 and L2 of the overlappedbeams as shown are added, the result is substantially equal to a peakvalue L3 of the beam energy density. Then, energy densities are leveledamong the centers of the ovals.

Ideally, the result of the addition of L1 and L2 is equal to L3.However, in reality, they are not always equal. An acceptable range of adifference between a value. obtained by adding L1 and L2 and L3 can beset by a designer properly.

When a laser beam is used independently; the energy density distributionfollows the Gaussian distribution. Therefore, laser light having uniformenergy densities is difficult to irradiate to an entire part, which is asemiconductor film or an island in contact with a flat part of aninsulating film. However, as shown in FIG. 18D, multiple laser lightbeams are overlapped so as to compensate each other for parts havinglower energy densities. Thus, the area having uniform energy densitybecomes larger than the area obtained by using laser light beamsindependently. Therefore, the crystallinity of the semiconductor filmcan be improved efficiently.

FIGS. 19A and 19B show calculated distributions of energy densitiestaken at dotted lines B-B′ and C-C′ in FIG. 18C. In FIGS. 19A and 19B,the reference is an area satisfying an energy density of a laser beambefore combined at 1/e² of the peak value. In the laser beam beforecombined, a length in the minor axis direction is 37 μm and a length inthe major axis direction is 410 μm. A distance between centers is 192μM. In this case, the energy densities at B-B′ and C-C′ havedistributions as shown in FIGS. 19A and 19B, respectively. Though thedistribution at B-B′ is slightly smaller than the distribution at C-C′,they can be regarded as the same size. Therefore, the form of thecombined laser beam can be regarded as being linear in an areasatisfying the energy density equal to 1/e² of the peak value of thelaser beam before combined.

FIG. 20 is a diagram showing an energy distribution of a combined laserbeam. An area 361 has a uniform energy density. An area 362 has a lowerenergy density. In FIG. 20, a length in a center axis direction of alaser beam is W_(TBW) while a length in the center axis direction in thearea 361 having the uniform energy density is W_(max). As the lengthW_(TBW) is longer than the length W_(max), the percentage of the area362 having the energy density which is not uniform and cannot be usedfor semiconductor crystallization, becomes larger to the area 361 havinguniform energy density, which can be used for the crystallization. Whenonly the area 362 whose energy density is not uniform is irradiated,micro crystal is generated. Then, the crystallinity of the semiconductorfilm is not high. Accordingly, scanning paths and depressions andprojections of the insulating film must be arranged so as to prevent theisland area of the semiconductor film and only the area 362 fromoverlapping. Then, as the percentage of the area 362 to the area 361 islarger, the limitation becomes larger. Using a slit can prevent only thearea 362 whose energy density is not uniform from being irradiated to asemiconductor film formed on a depression of the insulating film. Then,the limitations on arrangement of scanning paths and depressions andprojections of the insulating film can be effectively reduced.

This example can be implemented in combination with the first toeleventh examples.

Thirteenth Example

In this example, an optical system of a laser irradiation apparatus usedin the present invention and a positional relationship between eachoptical system and a slit will be described.

FIG. 21 shows an optical system used when four laser beams are combinedto one laser beam. The optical system shown in FIG. 21 has sixcylindrical lenses 417 to 422. Four laser light beams emitted fromdirections indicated by arrows enter to four cylindrical lenses 419 to422. Forms of two laser light beams formed by the cylindrical lenses 419and 421 are shaped by the cylindrical lens 417 again. Then, the laserlight beams are irradiated to an object 423 through a slit 424. On theother hand, the two laser light beams shaped by the cylindrical lenses420 and 422 are shaped by the cylindrical lens 418 again. Then, thelaser light beams are irradiated to the object 423 through the slit 424.

The laser light laser beams on the object 423 are overlapped and arecombined partially with each other to form one laser beam.

The focus distance and incident angle of each lens can be set by adesigner properly. The focus distance of the cylindrical lenses 417 and418 closest to the object 423 is designed to be smaller than the focusdistance of the cylindrical lenses 419 to 422. For example, the focusdistance of the cylindrical lenses 417 and 418 closest to the object 423is 20 mm. The focus distance of he cylindrical lenses 419 to 422 is 150mm. In this example, each of the lenses are set such that the incidentangle of laser light from the cylindrical lenses 417 and 418 to theobject 400 can be 25° and the incident angle of laser light from thecylindrical lenses 419 to 422 to the cylindrical lenses 417 and 418 canbe 10°. In order to prevent return light and to perform uniformirradiation, the incident angle of the laser light to the substrate ismaintained larger than 0° and desirably 5 to 30°.

FIG. 21 shows an example for combining four laser beams. In this case,four cylindrical lenses corresponding to four laser oscillating devices,respectively, and two cylindrical lenses corresponding to the fourcylindrical lenses are provided. However, the number of laser beams tobe combined is not limited thereto. Two to eight laser beams may becombined. If n laser beams are combined (where n=2, 4, 6 or 8), ncylindrical lenses corresponding to n laser oscillating devices,respectively, and n/2 cylindrical lenses corresponding to the ncylindrical lenses are provided. If n laser beams are combined (wheren=3, 5 or 7), n cylindrical lenses corresponding to n laser oscillatingdevices, respectively, and (n+1)/2 cylindrical lenses corresponding tothe n cylindrical lenses are provided.

If five or more laser beams are overlapped, the fifth and subsequentlaser light beam are desirably irradiated from the opposite side of thesubstrate in view of a place where the optical system is placed, theinterference and so on. In this case, the slit must be provided also inthe opposite side of the substrate. The substrate must havetransmittance.

In order to prevent return light from returning by tracing the originallight path, the incident angle to the substrate is desirably maintainedlarger than 0° and smaller than 90°.

In order to irradiate uniform laser light, the incident plane must beperpendicular to the irradiated surface and include a short side or along side of a rectangular, which is formed by each beam beforecombined. Then, an incident angle θ of the laser light desirablysatisfies θ>arctan (W/2d) where W is a length of the short side or thelong side included in the incident plane and d is a thickness of asubstrate which is placed on the irradiated surface and is translucentto the light laser light. The equation must be satisfied for each laserlight before combined. When the laser light path is not on the incidentplane, the incident angle of path projected onto the incident plane isthe incident angle θ. If laser light is entered at the incident angle θ,the light reflected by the substrate surface and the light reflectedfrom the back surface of the substrate do not interfere. Therefore,uniform laser light can be irradiated. In this discussion, therefractive index of the substrate is 1. In reality, most substrates havethe refractive index of around 1.5. In consideration of the value, alarger calculated value can be obtained than an angle calculatedaccording to this discussion. However, energy at both longitudinal endsof a beam spot is attenuated. Therefore, the interference does notaffect on this part very much, and the sufficient effect of interferenceattenuation can be obtained with the calculated value.

The optical system having the laser irradiating apparatus used in thepresent invention is not limited to the construction described in thisexample.

This example can be implemented in combination with first to twelfthexamples.

Fourteenth Example

Laser light having an oval-shaped laser beam has an energy densitydistribution following the Gaussian distribution in a directionperpendicular to the scanning direction. Therefore, the percentage ofthe low energy density area in the total area is higher than that of thelaser light having a rectangular or linear laser beam. Thus, in thepresent invention, the rectangular or linear laser beam of the laserlight is desirable which has a more uniform energy density distribution.

Excimer laser and slab laser are typical gas laser and solid laser,respectively, which can obtain a rectangular or linear laser beam. Inthis example, the slab laser will be described.

FIG. 22A shows an example of a construction of a slab type laseroscillating device. The slab type laser oscillating device shown in FIG.22A has a rod 7500, a reflection mirror 7501, an output mirror 7502, anda cylindrical lens 7503.

When excited light is irradiated to the rod 7500, the excited lighttraces a zigzag optical path within the rod 7500. Then, laser light isemitted to the reflection mirror 7501 or output mirror 7502 side. Thelaser light emitted to the reflection mirror 7501 side is reflected andenters into the rod 7500 again. Then, the laser light is emitted to theoutput mirror 7502 side. The rod 7500 is of slab type using aplate-shaped slab medium. By using the slab type rod 7500, a longer orlinear laser beam can be formed when emitted. The emitted laser light isprocessed in the cylindrical lens 7503 such that the form of the laserbeam can be narrower Then, the laser beam is emitted from the laseroscillating device.

FIG. 22B shows another construction of the slab type laser oscillatingdevice, which is different from the one shown in FIG. 22A. Theconstruction in FIG. 22B is different from the one in FIG. 22A in that acylindrical lens 7504 is added to the laser oscillating device. A lengthof laser beams can be controlled by using the cylindrical lens 7504.

The laser beam can become narrower when a coherent length is 10 cm ormore and preferably 1 m or more.

In order to prevent an excessive -increase in temperature of the rod7500, a device for controlling a temperature may be provided forcirculating cooling water, for example.

FIG. 22C shows an example of a form of a cylindrical lens. A cylindricallens 7509 in this example is fixed by a holder 7510. The cylindricallens 7509 has a cylinder surface and a rectangle plane, which are facingagainst each other. Two buses of the cylinder surface and two sides ofthe facing rectangle are all parallel with each other. Two planes formedby the two buses of the cylinder surface and the parallel two sides,respectively, cross with the plane of the rectangle at an angle largerthan 0° and smaller than 90°. When the two planes formed by the twoparallel sides, respectively, cross with the plane of the rectangle atan angle smaller than 90°, a shorter focus distance can be obtained thanthat obtained by crossing at an angle of 90° or more. Then, the form oflaser beams becomes narrower and can be closer to linear laser beams.

This example can be implemented in combination with the first tothirteenth examples.

Fifteenth Example

In this example, a relationship between a distance between centers oflaser beams and an energy density when laser beams are overlapped.

In FIG. 23, distributions of energy densities in the center axisdirection of laser beams and distributions of energy densities ofcombined laser beams are indicated by solid lines and dotted lines,respectively. Values of energy densities in the center axis direction oflaser beams generally follow the Gaussian distribution.

When a distance in the center axis direction satisfying an energydensity equal to or more than 1/e² of a peak value in a laser beambefore combined is 1, a distance between peaks is X. In a combined laserbeam, an increased amount between a peak value after combined and anaverage of valley values is Y. A relationship between X and Y obtainedby simulation is shown in FIG. 24. Y is expressed in percentage in FIG.24.

In FIG. 24, the energy difference Y is expressed in an approximateexpression of the following Equation 1:Y=60−293X+340X ²  [Eq. 1](where X is a larger one of two solutions)

According to Equation 1, when an energy difference needs to be about 5%,for example, X is about 0.584. Ideally, Y=0, which is difficult toachieve in reality. Thus, a designer must set an acceptable range of theenergy difference Y appropriately. Though Y=0 is ideal, the length of abeam spot becomes shorter. Therefore, X may be determined in view of thebalance with the throughput.

Next, the acceptable range of Y will be described. FIG. 25 showsdistributions of outputs (W) of YVO₄ laser to beam width in the centeraxis direction when the laser beam is oval. A shaded area is a range ofoutput energy required for obtaining good crystallinity. The combinedlaser light output energy only needs to be in the range of 3.5 to 6 W.

When a maximum value and a minimum value of output energy of a combinedbeam spot barely falls in the output energy range required for obtaininggood crystallinity, the energy difference Y for obtaining goodcrystallinity is maximum. Therefore, in FIG. 25, the energy difference Yis ±26.3%. The energy difference Y only needs to fall in the range forobtaining good crystallinity.

The range of output energy for obtaining good crystallinity depends onthe acceptable good crystallinity range. The distribution of outputenergy also depends on laser beam form. Thus, the acceptable range ofthe energy difference Y is not always limited to the values. Thedesigner must define a range of output energy required for goodcrystallinity appropriately. Then, the acceptable range of the energydifference Y must be defined based on the distribution of output energyof used laser.

This example can be implemented in combination with the first tofourteenth examples.

Sixteenth Example

A multi-channel TFT of the semiconductor device according to the presentinvention can have smaller variations in S-value, mobility, thresholdvalue and so on than those of a single-channel TFT and a multi-channelTFT formed by using crystallized semiconductor film.

FIG. 45A shows a frequency distribution of S-values of the n-typemulti-channel TFT according to the present invention. The multi-channelTFT according to the present invention has a semiconductor filmcrystallized by laser light irradiation on an insulating film havingdepressions and projections. Widths of each of the projections anddepressions of the insulating film are 1.25 μM and 1.50 μm,respectively. A channel length of the TFT is 8 μm, and the total channelwidth is 12 μm.

For comparison, FIG. 45B shows a frequency distribution of S-values ofan n-type single channel TFT crystallized on a flat insulating film.Both channel length and channel width of the TFT are 8 μm. FIG. 45Cshows a frequency distribution of S-values of an n-type multi-channelTFT crystallized on a flat insulating film. In the TFT, a channel lengthis 8 μm. The total channel width is 12 μm. A width of each channel is 2μm. A space between channels is 2 μm.

The standard deviation is σ=15.8 mV/dec. in FIG. 45B, and the standarddeviation is σ=19.9 mV/dec. in FIG. 45C. On the other hand, the standarddeviation in FIG. 45A is σ=8.1 mV/dec., which is smaller than the othertwo values. Therefore, the n-type multi-channel TFT according to thepresent invention shown in FIG. 45A has the smaller variation inS-values.

The channel width of the TFT in FIG. 45B is shorter than the totalchannel width of the TFT in FIG. 45A. In the TFT in FIG. 45C, the widthof each channel and the space between channels are longer than those inthe TFT in FIG. 45A. However, even in consideration of these conditions,the standard deviation in FIG. 45A may be significantly smaller thanthose in FIGS. 45B and 45C. Therefore, the n-channel type TFT accordingto the present invention can have smaller S-values.

Next, FIG. 46A shows a frequency distribution of threshold values of then-type multi-channel TFT according to the present invention. Theconstruction of the “TFT” in FIG. 46A is the same as that in FIG. 45A.For comparison, FIG. 46B shows a frequency distribution of thresholdvalues of an n-type single channel TFT crystallized on a flat insulatingfilm. The construction of the “TFT” in FIG. 46B is the same as that inFIG. 45B. FIG. 46C shows a frequency distribution of threshold values ofan n-type multi-channel IFT crystallized on a flat insulating film. Theconstruction of the TFT in FIG. 46C is the same as that in FIG. 45B.

The standard deviation is σ=126 mV/dec. in FIG. 46B, and the standarddeviation is σ=153 mV/dec. in FIG. 46C. On the other hand, the standarddeviation in FIG. 46A is σ=80 mV/dec., which is smaller than the othertwo values. Therefore, the n-type multi-channel TFT according to thepresent invention shown in FIG. 46A has the smaller variation inthreshold values.

The channel width of the TFT in FIG. 46B is shorter than the totalchannel width of the TFT in FIG. 46A. In the TFT in FIG. 46C, the widthof each channel and the space between channels are longer than those inthe TFT in FIG. 46A. However, even in consideration of these conditions,the standard deviation in FIG. 46A may be significantly smaller thanthose in FIGS. 46B and 46C. Therefore, the n-channel type TFT accordingto the present invention can have smaller threshold values.

Next, FIG. 47A shows a frequency distribution of mobility of the n-typemulti-channel TFT according to the present invention. The constructionof the TFT in FIG. 47A is the same as that in FIG. 45A. For comparison,FIG. 47B shows a frequency distribution of mobility of an n-type singlechannel TFT crystallized on a flat insulating film. The construction ofthe TFT in FIG. 47B is the same as that in FIG. 45B. FIG. 47C shows afrequency distribution of mobility of an n-type multi-channel TFTcrystallized on a flat insulating film. The construction of the TFT inFIG. 47C is the same as that in FIG. 45B.

The standard deviation is σ=7.9% in FIG. 47B, and the standard deviationis σ=9.2% in FIG. 47C. On the other hand, the standard deviation in FIG.47A is σ=5.2%, which is smaller than the other two values. Therefore,the n-type multi-channel TFT according to the present invention shown inFIG. 47A has the smaller variation in mobility. In FIG. 47A, themobility is calculated by using a design value of the channel width.Therefore, the actual mobility may be lower by about 20%.

The channel width of the TFT in FIG. 47B is shorter than the totalchannel width of the TFT in FIG. 47A. In the TFT in FIG. 47C, the widthof each channel and the space between channels are longer than those inthe TFT in FIG. 47A. However, even in consideration of these conditions,the standard deviation in FIG. 47A may be significantly smaller thanthose in FIGS. 47B and 47C. Therefore, the n-channel type TFT accordingto the present invention can have smaller mobility.

Next, FIG. 48A shows a frequency distribution of threshold values of thep-type multi-channel TFT according to the present invention. Theconstruction of the TFT in FIG. 48A is the same as that in FIG. 45A. Forcomparison, FIG. 48B shows a frequency distribution of threshold valuesof a p-type single channel TFT crystallized. on a flat insulating film.The construction of the TFT in FIG. 48B is the same as that in FIG. 45Bexcept that the polarities are different. FIG. 48C shows a frequencydistribution of threshold values of a p-type multi-channel TFTcrystallized on a flat insulating film. The construction of the TFT inFIG. 48C is the same as that in FIG. 45B except that the polarities aredifferent.

The standard deviation is σ=218 mV in FIG. 48B, and the standarddeviation is σ=144 mV in FIG. 48C. On the other hand, the standarddeviation in FIG. 48A is σ=77 mV, which is smaller than the other twovalues. Therefore, the p-type multi-channel TFT according to the presentinvention shown in FIG. 48A has the smaller variation in thresholdvalues.

The channel width of the TFT in FIG. 48B is shorter than the totalchannel width of the TFT in FIG. 48A. In the TFT in FIG. 48C, the widthof each channel and the space between channels are longer than those inthe TFT in FIG. 48A. However, even in consideration of these conditions,the standard deviation in FIG. 48A may be significantly smaller thanthose in FIGS. 48B and 48C. Therefore, the p-channel type TFT accordingto the present invention can have smaller threshold values.

Next, FIG. 49A shows a frequency distribution of mobility of the p-typemulti-channel TFT according to the present invention. The constructionof the TFT in FIG. 49A is the same as that in FIG. 45A except that thepolarities are different. For comparison, FIG. 49B shows a frequencydistribution of mobility of a p-type single channel TFT crystallized ona flat insulating film. The construction of the TFT in FIG. 49B is thesame as that in FIG. 45B except that the polarities are different. FIG.49C shows a frequency distribution of mobility of a p-type multi-channelTFT crystallized on a flat insulating film. The construction of the TFTin FIG. 49C is the same as that in FIG. 45B except that the polaritiesare different.

The standard deviation is σ=7.6% in FIG. 49B, and the standard deviationis σ=5.9% in FIG. 49C. On the other hand, the standard deviation in FIG.49A is σ=4.6%, which is smaller than the other two values. Therefore,the p-type multi-channel TFT according to the present invention shown inFIG. 49A has the smaller variation in. mobility. In FIG. 49A, themobility is calculated by using a design value of the channel width.Therefore, the actual mobility may be lower by about 20%.

The channel width of the TFT in FIG. 49B is shorter than the totalchannel width of the TFT in FIG. 49A. In the TFT in FIG. 49C, the widthof each channel and the space between channels are longer than those inthe TFT in FIG. 49A. However, even in consideration of these conditions,the standard deviation in FIG. 49A may be significantly smaller thanthose in FIGS. 49B and 49C. Therefore, the p-channel type TFT accordingto the present invention can have smaller mobility.

As shown in FIG. 45A to 49C, the multi-channel TFT according to thepresent invention can suppress the variations in characteristics. Thecrystal orientation of each channel can rotate more easily than those ina single-channel TFT and a multi-channel TFT crystallized on a flatinsulating film. Therefore, various crystal orientations are included.Thus, the variations in characteristics due to the crystal orientationsmay be easily leveled off.

Seventeenth Example

In this example, a construction of the present invention will bedescribed for forming an insulating film on a rectangular orstrip-shaped gate electrode so as to provide depressions and projectionson the surface of the insulating film.

First of all, as shown in FIG. 50A, a conductive film is formed and thenis patterned on a substrate 7000. Thus, first rectangular gateelectrodes 7001 and 7002 are formed. The thickness of the first gateelectrodes 7001 and 7002 is desirably about 40 to 150 nm. The first gateelectrodes 7001 and 7002 have a stripe form.

Next, a first gate insulating film 7003 is formed on the substrate 7000so as to cover the first gate electrodes 7001 and 7002. The thickness ofthe first gate insulating film 7003 is desirably about 40 to 150 nm. Thesurface of the first gate insulating film 7003 has depressions andprojections due to the existence of the rectangular first gateelectrodes 7001 and 7002. The width of each of the projections isdesirably 1 to 10 μm, and the width of each of the depressions isdesirably 0.5 to 10 μm. The first gate electrodes 7001 and 7002 areplaced such that they can fall in the ranges.

Next, a semiconductor film 7004 is formed on the first gate insulatingfilm 7003 (FIG. 50B). The thickness of the semiconductor film 7004 isdesirably about 60 to 200 nm.

Next, by irradiating laser light to the semiconductor film 7004, apolycrystalline semiconductor film having improved crystallinity isformed as shown in FIG. 50C. The polycrystalline semiconductor film ismelted by the irradiation of laser light and volume-moves into thedepression of the first gate insulating film 7003. Then, the projectionof the first gate insulating film 7003 is exposed. The polycrystallinesemiconductor film is patterned to form an island-shape semiconductorfilm 7005 (FIG. 50C).

Next, a second gate insulating film 7006 is formed such that it cancover the island-shaped semiconductor film 7005 (FIG. 50D). The firstgate insulating film 7003 and the second gate insulating film 7006 areetched partially to form a contact hole. Then, the first gate electrodes7001 and 7002 are exposed partially.

Next, a conductive film is formed and is patterned such that theconductive form can cover the exposed parts of the first gate electrodes7001 and 7002 and the second gate insulating film 7006. As a result, asecond gate electrode 7007 is formed which is connected to the firstgate electrodes 7001 and 7002 in the contact hole.

Then, an impurity giving conductivity is doped to the island-shapedsemiconductor film 7005 such that a channel forming region can be formedat a part where the semiconductor film 7005 and the second gateelectrode 7007 overlap with each other through the second gateinsulating film 7006. In this example, a mask of resist is formedthereon for doping several times. Thus, a first impurity region 7008functioning as a source/drain region and a second impurity region 7009functioning as an LDD region are formed (FIG. 50E).

FIG. 50F is a top view of the TFT in the state shown in FIG. 50E. FIG.50E is a section diagram taken at a line A-A′ in FIG. 50F. FIG. 50G is asection diagram taken at a line B-B′ in FIG. 50E A region 7010 shown inFIG. 50G corresponds to a channel forming region. The channel formingregion 7010 overlaps with the first gate electrodes 7001 and 7002through the first gate insulating film 7003. The channel forming region7010 overlaps with the second gate electrode 7007 through the secondgate insulating film 7006.

The TFT having the construction described in this example has channelsnot only near the top surface of the channel forming region 7010 butalso near both side surfaces. Therefore, ON-current can be increased.

In FIG. 50C, the projection of the first gate insulating film 7003 isexposed. However, depending on the thickness of the formed semiconductorfilm 7004, the island-shaped semiconductor film 7005 may cover theprojection of the first gate insulating film 7003. In this case,additionally, the surface of the island-shaped semiconductor film 7005is etched. Then, the projection of the first gate insulating film 7003is exposed.

1. A semiconductor device comprising: a primary insulating film having adepression formed over a substrate; and a crystalline semiconductor filmhaving source and drain regions and a channel forming region between thesource and drain regions, wherein the channel forming region is formedon a bottom of the depression of the primary insulating film, andwherein the channel forming region extends along one line of thedepression.
 2. A semiconductor device comprising: an insulating filmcomprising at least one of silicon nitride, silicon nitride oxide,silicon oxide and silicon oxide nitride and having a depression; and acrystalline semiconductor film having source and drain regions and achannel forming region between the source and drain regions, wherein thechannel forming region is formed on a bottom of the depression of theinsulating film, and wherein the channel forming region extends alongone line of the depression.
 3. A semiconductor device comprising: a thinfilm transistor in which a plurality of channel forming regions areprovided in parallel in a crystalline semiconductor film, wherein theplurality of channel forming regions are formed on a bottom of each of aplurality of depressions of a primary insulating film, respectively,wherein each of the channel forming regions extends along one line ofthe depressions and connects to the plurality of channel formingregions, and wherein a source or drain region is formed in a crystallinesemiconductor film formed continuously with the crystallinesemiconductor film.
 4. A semiconductor device comprising: a thin filmtransistor in which a plurality of channel forming regions are providedin parallel in a crystalline semiconductor film, wherein the pluralityof channel forming regions are formed on a bottom of each of a pluralityof depressions of a primary insulating film, respectively, wherein eachof the channel forming regions extends along one line of the depressionsand connects to the plurality of channel forming regions, and wherein asource or drain region is formed in a crystalline semiconductor filmformed continuously with the crystalline semiconductor film andextending from the bottom of the depression to a top of a projection. 5.A semiconductor device comprising: a thin film transistor in which aplurality of channel forming regions are provided in parallel in acrystalline semiconductor film, wherein the plurality of channel formingregions are formed on a bottom of each of a plurality of noncyclicdepressions of a primary insulating film, respectively, wherein each ofthe channel forming regions extends along one line of the depression andconnects to the plurality of channel forming regions, and wherein asource or drain region is formed in a crystalline semiconductor filmformed continuously with the crystalline semiconductor film andextending from the bottom of the depression to a top of a projection. 6.A semiconductor device according to claim 3, wherein the primaryinsulating film has a grade change having a first insulating film ofsilicon oxide or silicon oxide nitride and a second insulating film ofsilicon nitride or silicon nitride oxide formed on the first insulatingfilm.
 7. A semiconductor device according to claim 4, wherein theprimary insulating film has a grade change having a first insulatingfilm of silicon oxide or silicon oxide nitride and a second insulatingfilm of silicon nitride or silicon nitride oxide formed on the firstinsulating film.
 8. A semiconductor device according to claim 5, whereinthe primary insulating film has a grade change having a first insulatingfilm of silicon oxide or silicon oxide nitride and a second insulatingfilm of silicon nitride or silicon nitride oxide formed on the firstinsulating film.
 9. A semiconductor device according to claim 3, whereinthe primary insulating film has a grade change having a first insulatingfilm of silicon oxide or silicon oxide nitride and a second insulatingfilm of silicon nitride or silicon nitride oxide formed on the firstinsulating film.
 10. A semiconductor device according to claim 4,wherein the primary insulating film has a grade change having a firstinsulating film of silicon oxide or silicon oxide nitride and a secondinsulating film of silicon nitride or silicon nitride oxide formed onthe first insulating film.
 11. A semiconductor device according to claim5, wherein the primary insulating film has a grade change having a firstinsulating film of silicon oxide or silicon oxide nitride and a secondinsulating film of silicon nitride or silicon nitride oxide formed onthe first insulating film.
 12. A semiconductor device comprising: aplurality of first gate electrodes; a first gate insulating filmcovering the plurality of first gate electrodes and having depressionsand projections on the surface; a crystalline semiconductor film havinga channel forming region of each of the depressions of the first gateinsulating film; a second gate insulating film formed on the crystallinesemiconductor film and being in contact with the projections of thefirst gate insulating film; and a second gate electrode formed on thesecond gate insulating film and being in contact with the plurality offirst gate electrodes through contact holes in the first and second gateinsulating films, wherein the channel forming region overlaps with anytwo of the plurality of first gate electrodes through the first gateinsulating film and overlaps with the second gate electrode through thesecond gate insulating film.
 13. A semiconductor device comprising: aprimary insulating film over a substrate; and a thin film transistorhaving a crystalline semiconductor film over the primary insulatingfilm, wherein a channel forming region in the crystalline semiconductorfilm is formed on a bottom of the depression of the primary insulatingfilm, and wherein the channel forming region extends along one line ofthe depression.
 14. A semiconductor device according to claim 1, whereinthe semiconductor device is incorporated into an electronic apparatusselected from the group consisting of a mobile information terminal, avideo camera, a digital camera, a personal computer, a televisionreceiver, a mobile telephone and a projecting type display apparatus.15. A semiconductor device according to claim 2, wherein thesemiconductor device is incorporated into an electronic apparatusselected from the group consisting of a mobile information terminal, avideo camera, a digital camera, a personal computer, a televisionreceiver, a mobile telephone and a projecting type display apparatus.16. A semiconductor device according to claim 3, wherein thesemiconductor device is incorporated into an electronic apparatusselected from the group consisting of a mobile information terminal, avideo camera, a digital camera, a personal computer, a televisionreceiver, a mobile telephone and a projecting type display apparatus.17. A semiconductor device according to claim 4, wherein thesemiconductor device is incorporated into an electronic apparatusselected from the group consisting of a mobile information terminal, avideo camera, a digital camera, a personal computer, a televisionreceiver, a mobile telephone and a projecting type display apparatus.18. A semiconductor device according to claim 5, wherein thesemiconductor device is incorporated into an electronic apparatusselected from the group consisting of a mobile information terminal, avideo camera, a digital camera, a personal computer, a televisionreceiver, a mobile telephone and a projecting type display apparatus.19. A semiconductor device according to claim 12, wherein thesemiconductor device is incorporated into an electronic apparatusselected from the group consisting of a mobile information terminal, avideo camera, a digital camera, a personal computer, a televisionreceiver, a mobile telephone and a projecting type display apparatus.20. A semiconductor device according to claim 13, wherein thesemiconductor device is incorporated into an electronic apparatusselected from the group consisting of a mobile information terminal, avideo camera, a digital camera, a personal computer, a televisionreceiver, a mobile telephone and a projecting type display apparatus.21. A semiconductor device comprising; a primary insulating film over asubstrate; two second insulating films over the primary insulating film;and, a crystalline semiconductor film comprising a source and drainregions and a channel forming region between the source and drainregions; wherein the channel forming region is formed on the primaryinsulating film, and exists between the two second insulating film. 22.A semiconductor device producing system, comprising: a laser oscillatingdevice; an optical system for gathering laser light oscillated from thelaser oscillating device such that the laser beam can be linear; firstmeans for moving a position to which the gathered laser light isirradiated; second means for forming an insulating film havingdepressions and projections on a substrate; third means for forming asemiconductor film on the insulating film; fourth means for storingpattern information of the insulating film; fifth means for determininga scanning path of the laser beam such that the scanning path caninclude the depressions of the semiconductor film based on the patterinformation with reference to a marker formed on the substrate and forcontrolling the first means to move the laser beam by following thescanning path for improving crystallinity of the semiconductor film; andsixth means for patterning the semiconductor film having improvedcrystallinity to form an island having channel forming regions on thedepressions of the insulating film.
 23. A semiconductor device producingsystem, comprising: a laser oscillating device; an optical system forgathering laser light oscillated from the laser oscillating device suchthat the laser beam can be linear; first means for moving a position towhich the gathered laser light is irradiated; second means for formingan insulating film having depressions and projections on a substrate;third means for forming a semiconductor film on the insulating film;fourth means for storing pattern information of the insulating film;fifth means for determining a scanning path of the laser beam such thatthe scanning path can include the depressions of the semiconductor filmbased on the pattern information and a width in a directionperpendicular to a scanning direction of the laser beam with referenceto a marker formed on the substrate and for controlling the first meansto move the laser beam by following the scanning path for improvingcrystallinity of the semiconductor film; and sixth means for patterningthe semiconductor film having improved crystallinity to form an islandhaving channel forming regions on the depressions of the insulatingfilm.
 24. A semiconductor device producing system comprising: a laseroscillating device; an optical system for gathering laser lightoscillated from the laser oscillating device such that the laser beamcan be linear; first means for moving a position to which the gatheredlaser light is irradiated; second means for storing input patterninformation; third means for forming an insulating film havingdepressions and projections on a substrate in accordance with thepattern information; fourth means for forming a semiconductor film onthe insulating film; fifth means for reading pattern information of theformed semiconductor film; sixth means for storing the read patterninformation; seventh means for determining a scanning path of the laserbeam such that the scanning path includes the depressions of thesemiconductor film based on pattern information stored in the secondmeans or pattern information stored in the sixth means with reference topositional information of the substrate obtained from the patterninformation stored in the second means and the pattern informationstored in the sixth means and for controlling the first means to movethe laser beam by following the scanning path for improvingcrystallinity of the semiconductor film; and eighth means for patterningthe semiconductor film having improved crystallinity to form an islandhaving channel forming regions on the depressions of the insulatingfilm.
 25. A semiconductor device producing system according to claim 24,wherein the fifth means uses a charge-coupled device.
 26. Asemiconductor device producing system comprising: a laser oscillatingdevice; an optical system for gathering laser light oscillated from thelaser oscillating device such that the laser beam can be linear; firstmeans for moving a position to which the gathered laser light isirradiated; second means for forming an insulating film havingdepressions and projections on a substrate; third means for forming asemiconductor film on the insulating film; fourth means for storingpattern information of the insulating film; fifth means for determininga scanning path of the laser beam such that the scanning path caninclude the depressions of the semiconductor film based on the patterninformation with reference to a marker formed on the substrate and forcontrolling the first means to move the laser beam by following thescanning path for improving crystallinity of the semiconductor film; andsixth means for patterning the semiconductor film having improvedcrystallinity to form an island spanning depressions of the insulatingfilm, wherein the channel forming regions of the island are provided onthe depressions and are separated from each other.
 27. A semiconductordevice producing system comprising: a laser oscillating device; anoptical system for gathering laser light oscillated from the laseroscillating device such that the laser beam can be linear; first meansfor moving a position to which the gathered laser light is irradiated;second means for forming an insulating film having depressions andprojections on a substrate; third means for forming a semiconductor filmon the insulating film; fourth means for storing pattern information ofthe insulating film; fifth means for determining a scanning path of thelaser beam such that the scanning path can include the depressions ofthe semiconductor film based on the pattern information and a width in adirection perpendicular to a scanning direction of the laser beam withreference to a marker formed on the substrate and for controlling thefirst means to move the laser beam by following the scanning path forimproving crystallinity of the semiconductor film; and sixth means forpatterning the semiconductor film having improved crystallinity to forman island spanning depressions of the insulating film, wherein thechannel forming regions of the island are provided on the depressionsand are separated from each other.
 28. A semiconductor device producingsystem comprising: a laser oscillating device; an optical system forgathering laser light oscillated from the laser oscillating device suchthat the laser beam can be linear; first means for moving a position towhich the gathered laser light is irradiated; second means for storinginput pattern information; third means for forming an insulating filmhaving depressions and projections on a substrate in accordance with thepattern information; fourth means for forming a semiconductor film onthe insulating film; fifth means for reading pattern information of theformed semiconductor film; sixth means for storing the read patterninformation; seventh means for determining a scanning path of the laserbeam such that the scanning path includes the depressions of thesemiconductor film based on pattern information stored in the secondmeans or pattern information stored in the sixth means with reference topositional information of the substrate obtained from the patterninformation stored in the second means and the pattern informationstored in the sixth means and for controlling the first means to movethe laser beam by following the scanning path for improvingcrystallinity of the semiconductor film; and eighth means for patterningthe semiconductor film having improved crystallinity to form an islandspanning depressions of the insulating film, wherein the channel formingregions of the island are provided on the depressions and are separatedfrom each other.
 29. A semiconductor device producing system accordingto claim 28, wherein the fifth means uses a charge-coupled device.
 30. Asemiconductor device producing system according to claim 22, whereinlaser light scanning is performed in a reduced pressure atmosphere or inan atmosphere of inactive gas.
 31. A semiconductor device producingsystem according to claim 23, wherein laser light scanning is performedin a reduced pressure atmosphere or in an atmosphere of inactive gas.32. A semiconductor device producing system according to claim 24,wherein laser light scanning is performed in a reduced pressureatmosphere or in an atmosphere of inactive gas.
 33. A semiconductordevice producing system according to claim 26, wherein laser lightscanning is performed in a reduced pressure atmosphere or in anatmosphere of inactive gas.
 34. A semiconductor device producing systemaccording to claim 27, wherein laser light scanning is performed in areduced pressure atmosphere or in an atmosphere of inactive gas.
 35. Asemiconductor device producing system according to claim 28, whereinlaser light scanning is performed in a reduced pressure atmosphere or inan atmosphere of inactive gas.
 36. A semiconductor device producingsystem according to claim 22, wherein the laser light is output by usingone or multiple kinds selected from YAG laser, YVO4 laser, YLF laser,YAlO3 laser, glass laser, ruby laser, alexandrite laser, Ti:sapphirelaser, or Y2O3 laser.
 37. A semiconductor device producing systemaccording to claim 23, wherein the laser light is output by using one ormultiple kinds selected from YAG laser, YVO4 laser, YLF laser, YAIO3laser, glass laser, ruby laser, alexandrite laser, Ti:sapphire laser, orY2O3 laser.
 38. A semiconductor device producing system according toclaim 24, wherein the laser light is output by using one or multiplekinds selected from YAG laser, YVO4 laser, YLF laser, YAIO3 laser, glasslaser, ruby laser, alexandrite laser, Ti:sapphire laser, or Y2O3 laser.39. A semiconductor device producing system according to claim 26,wherein the laser light is output by using one or multiple kindsselected from YAG laser, YVO4 laser, YLF laser, YAlO3 laser, glasslaser, ruby laser, alexandrite laser, Ti:sapphire laser, or Y2O3 laser.40. A semiconductor device producing system according to claim 27,wherein the laser light is output by using one or multiple kindsselected from YAG laser, YVO4 laser, YLF laser, YAlO3 laser, glasslaser, ruby laser, alexandrite laser, Ti:sapphire laser, or Y2O3 laser.41. A semiconductor device producing system according to claim 28,wherein the laser light is output by using one or multiple kindsselected from YAG laser, YVO4 laser, YLF laser, YAIO3 laser, glasslaser, ruby laser, alexandrite laser, Ti:sapphire laser, or Y2O3 laser.42. A semiconductor device producing system according to claim 22,wherein the laser light is output by using slab laser.
 43. Asemiconductor device producing system according to claim 23, wherein thelaser light is output by using slab laser.
 44. A semiconductor deviceproducing system according to claim 24, wherein the laser light isoutput by using slab laser.
 45. A semiconductor device producing systemaccording to claim 26, wherein the laser light is output by using slablaser.
 46. A semiconductor device producing system according to claim27, wherein the laser light is output by using slab laser.
 47. Asemiconductor device producing system according to claim 28, wherein thelaser light is output by using slab laser.
 48. A semiconductor deviceproducing system according to claim 22, wherein the laser light isoscillated continuously.
 49. A semiconductor device producing systemaccording to claim 23, wherein the laser light is oscillatedcontinuously.
 50. A semiconductor device producing system according toclaim 24, wherein the laser light is oscillated continuously.
 51. Asemiconductor device producing system according to claim 26, wherein thelaser light is oscillated continuously.
 52. A semiconductor deviceproducing system according to claim 27, wherein the laser light isoscillated continuously.
 53. A semiconductor device producing systemaccording to claim 28, wherein the laser light is oscillatedcontinuously.
 54. A semiconductor device producing system according toclaim 22, wherein the laser light is the second harmonic.
 55. Asemiconductor device producing system according to claim 23, wherein thelaser light is the second harmonic.
 56. A semiconductor device producingsystem according to claim 24, wherein the laser light is the secondharmonic.
 57. A semiconductor device producing system according to claim26, wherein the laser light is the second harmonic.
 58. A semiconductordevice producing system according to claim 27, wherein the laser lightis the second harmonic.
 59. A semiconductor device producing systemaccording to claim 28, wherein the laser light is the second harmonic.60. A semiconductor device producing system according to claim 22,wherein the depressions and projections have rectangular or stripeshape.
 61. A semiconductor device producing system according to claim23, wherein the depressions and projections have rectangular or stripeshape.
 62. A semiconductor device producing system according to claim24, wherein the depressions and projections have rectangular or stripeshape.
 63. A semiconductor device producing system according to claim26, wherein the depressions and projections have rectangular or stripeshape.
 64. A semiconductor device producing system according to claim27, wherein the depressions and projections have rectangular or stripeshape.
 65. A semiconductor device producing system according to claim28, wherein the depressions and projections have rectangular or stripeshape.